Cover of 'Mine Sweeping Manual'.




Mine Sweeping Manual
United States Navy
1917




Washington
Government Printing Office
1917






CONTENTS.

Chapter I. Introduction.
Chapter II. General description of passing the sweep.
Chapter III.    Sweeping installation and equipment.
Chapter IV.    Stations and duties.
Chapter V. In the mine field.
Chapter VII. Group sweeping.
Chapter IX. Sweep group evolutions.
Chapter X. Sweeping definitions.


MINE SWEEPING MANUAL.


CHAPTER I.

INTRODUCTION.

1. Mine sweeping is the act of removing anchored mines from their moorings by dragging the submerged bight of a steel wire through a mine field.

2. Two vessels, called mine sweepers, together forming a sweeping pair, under standard conditions tow this wire between them. The vessels steam at a distance apart about equal in yards to the number of

Figure 1, showing two mine sweepers with sweep wire attached between them.

Fig. 1.

fathoms of sweep wire out. The bight thus formed takes up against the mooring cables of any mines in its path and either drags the mines along with their anchors or, by seesawing, cuts the mine's mooring cable, letting the mine itself float to the surface, where it can be destroyed. It is also possible that the sweep wire itself may explode the mine.

3. Unless some means is taken to maintain the whole length of the sweep wire bight at a depth which will insure the removal of all mines dangerous to navigation in its path only the center of the bight will ride deep enough to catch mines, and there will be no certainty

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as to the exact limits of the channel swept clear. To obtain this certainty is the main object of sweeping operations.

4a. A device known as a water kite is therefore towed by each sweeper to force its respective end of the sweep wire down to the desired sweeping depth. A water kite dives to a certain depth in a water current just as an ordinary kite rides to a certain height in an air current. A ring on the end of a short pendant attached to this water kite acts as a fair lead for the sweep wire, which, from there to the opposite kite, sweeps wholly at or below the depth of the kite, thus sweeping the fall width of channel between the kites at their depth. The limits of the swept channel may be taken safely as being 50 yards inside the wake of each sweeper.

4b. The depth of the kite depends on the length of kite wire out the speed through the water, and the tension on the sweep wire. A depth of 6 fathoms for the kite is desirable and is usually obtained under standard conditions, with 11 fathoms of kite wire out, at not above 10 knots.

5. When sweeping over a rocky bottom it is frequently necessary to hold the bight of the sweep wire up to a certain depth as well as to hold its ends down to this depth. Buoys attached to the bight by pendants are used for this purpose.

CHAPTER II.

GENERAL DESCRIPTION OF PASSING THE SWEEP.

6. The two boats of a sweeping pair are called the winch boat and slip boat, respectively, though the term is temporary only, as any sweeper may be assigned to either duty and must be prepared to act in either capacity at any time.

7. The winch boat uses her sweep wire for the sweeping, passing it over to the slip boat, which secures the end of it on board ready for slipping.

8. Preparations on both boats for sweeping -
(1)    Station the crew.
(2)    Rig out the kites.
(3)    Reeve off gear clear for running.
(4)    Test winches.
(5)    Take position preparatory to passing the sweep.

9. Special preparations on the winch boat. - (a) Unreel sufficient sweep wire to reeve it off through all fair leads and kite ring and thence to a point at the rail convenient for passing the end by means of heaving lines to the slip boat. Enough slack is stopped up along the rail to reach the slip boat, which has to haul the end aboard and secure it.

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Figure 2, showing two mine sweepers with sweep wire attached between them and kites.

Fig. 2.

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(a) Provide sweep buoys and means of attaching them to the sweep wire in case they are to be used.

(c) Pair off with the slip boat designated and take position 100 yards astern of her, ready for coming alongside and passing the sweep.

10. Special preparations on the slip boat. - (a) Secure the end of the shearing pin pendant in the pelican hook slip and reeve it through all fair leads, kite ring, and back to a point at the rail convenient for receiving the end of the sweep wire from the winch boat. At that point the sweep wire is to be joined to the shearing pin coupling and the pendant and the coupling then thrown clear astern.

(b) If the shearing pin coupling and pendant are not used, lead a receiving line from a winch gypsy through fair-leads and kite ring ready to bend on the end of the sweep wire when received. The sweep wire is then hauled through kite ring and fair-leads to the slip, in which it is directly secured. A light wire fitted with sister hooks is handy for this purpose and should be given a lead close to the pelican hook slip.

11. Passing the sweep. - (a) The two boats which have come alongside each other for the purpose of passing the sweep are now connected by the sweep wire. They immediately open out, the winch boat paying out the wire until she is at sweeping distance (standard 400 yards) from the slip boat, which has maintained course and reduced speed during the evolution.

(b) Both boats now lower kites into the water and proceed at standard speed with the sweeping on a previously designated course.

(c) The North Sea procedure is for the vessels to open out at full speed as soon as the end of the sweep wire is on the slip. As soon as the slip end is fast the winch boat opens out at full speed, the sweep wire "whistling out" off the winch drum and through the fair-leads and kite ring, its tension keeping the bight off the bottom. When out to distance, usually judged by eye, the winch boat makes a signal (blows whistle) to the slip boat, puts the sweep winch brake on; then, and not until then, the kites are lowered. The winch boat soon learns to judge by eye whether enough sweep wire is out by the direction of its lead off the quarter. The slip boat regulates her speed so that the pair may stand on at standard speed as soon as the winch boat is out to proper distance.

12. It is stated to be not uncommon to sweep with the bight dragging on the bottom, especially in channels that have been swept over day after day for months, all obstructions but mines and occasional wrecks having been thereby removed. Such a practice must depend on the character of the bottom and would not be possible on our New England coast, for instance. But rapid handling of the sweep is undoubtedly best for saving the sweep wire and for control

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of the vessels, as well as for getting the sweeping begun and carried on with reasonable dispatch.

13. Relative seniority of the sweeper captains does not affect the procedure, as either or any boat should at any time be free to take either slip or winch duty. Every sweeper must become well trained for both duties so that it will make no difference what boat she pairs with.

TACTICAL CONTROL.

14. Sweeping is usually carried out by groups of sweeping pairs, each group consisting of a guide boat and several pairs of sweepers. In case there is no special guide boat one of the sweepers is responsible for the course and sweeping speed of the sweeping group. It is usual for the winch boat to maintain position on the beam of the slip boat, which is responsible for the course and speed of the pair.

LEAD OF SWEEP.

15. (a) The sweep wire is best handled when led directly over the stern of each sweeper. On low-powered vessels, however, the drag of the wire will seriously interfere with the steering, so that it becomes necessary to lead the wire over from amidship or forward from some point near the pivoting point of the vessel. With this lead lizards and slip ropes are used to keep the wire clear of the propellers.

(b) Wherever fair leads are necessary casehardened roller chocks are installed. They should be of ample, stout dimensions, easily lubricated; and preferably of a standard size, so as to be interchangeable.

KITES.

16. (a) Water kites are rigged over the side or stern, ready for lowering into the water, on some form of gallows frame which permits an overhead lead for the kite wire.

(b) This kite wire may be a separate piece of wire (same size as the sweep wire) specially provided for the purpose; or, in vessels having two sweep wire drums, it may be the wire not in use as the sweep. The kite wire is led from the winch through fair-leads to the gallows frame and thence to the kite. In either case it must be led to some power appliance on deck so that the kite may be hauled up and hoisted on board.

(c) Sweepers thus have two wires leading from them into the water, viz, the sweep wire and the kite wire.

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CHAPTER III.

SWEEPING INSTALLATION AND EQUIPMENT.

17. A mine sweeper is any vessel equipped for the purpose of mine sweeping. Such a vessel should carry, for maximum efficiency, a special mine-sweeping winch and standard sweeping gear. She must be habitable for the required crew and have good sea-keeping qualities. The lightest possible draft is desirable.

18. Trawlers, large tugs, and yachts of between 400 and 1,200 tons, with maximum draft of 13 feet are suitable for equipment as mine sweepers. Specially designed vessels of 6 or 7 feet draft, paddle-wheel propulsion have been used in considerable number, especially for offshore work.

19. The principal item in the equipment of a sweeper is the sweeping winch. This should carry two sweep wires at least 600 fathoms long, of 13/16-inch diameter wire (2 1/2 inches circumference) on two separate drums. These, or either one at a time, may be disconnected from the driving shaft and controlled by a powerful hand brake when paying out the wire. They should be capable of heaving in at the rate of 600 feet per minute against a strain of 3 tons. All parts should be solid enough for any sudden strain sufficient to break the wire without injury to the winch.

When sweeping, one of these wires is used as the sweep wire, the other as the kite wire. The wires must not be crossed.

20. Sweepers not having such winches or having no power winch at all, may still sweep, but only with a much larger crew and then neither rapidly nor efficiently. The way to get the most out of such vessels, if they must be used, is to pair them off as slip boats with better equipped vessels as winch boats. The peculiarities of each vessel must be studied and the sweeping gear rigged accordingly, so as to sweep with standard conditions as nearly as possible.

21. The permanent sweeping installation on each sweeper should consist of -

1 special mine sweeping winch.
1 U or gallows frame for handling the kite.
1 set of bitts or heavy deck ring bolt for securing the sweep-wire slip. Fairlead roller chocks of standard design, in the number necessary.

22. The renewable equipment of a sweeper should consist of -

2 sweep wires 13/16 inch diameter, 600 fathoms each. (May be longer if the winch drum will take it.)
1 water kite, 12 feet or 9 feet.
2 kite wires 13/16 inch diameter, 30 fathoms. (Not required in vessels having a two-drum sweep winch.)
1 set spare parts for kite.

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3 kite rings of 2-inch case-hardened steel, 6 inches inside diameter.
4 shearing pin couplings.
2 shearing pin pendants, 13/16-inch wire, 40 fathoms.
100 shearing pins, 20,000 pounds. (This number may be reduced on stations where the bottom is generally free from rocks.)
2 pelican hook slips, 12 inches.
2 chain straps for same, 15/16 inch, 4 fathoms of chain in each strap.
4 buoys for sweep wire (strong beer casks fitted with wire slings and connecting shackle, or galvanized-steel buoys, about 29 inches diameter).
6 buoy pendants, 8 fathoms 1/2-inch diameter wire rope, eye splice in each end (3 1/2-inch manila may be substituted).
36 1/2-inch screw-pin shackles.
6 wire clamps (like Crosby or Dirigo clamps) for buoy stops; to take 13/16-inch wire.
12 channel sweeping spar or dan buoys.
12 500-pound sinkers.
12 buoy lines, 1/2-inch flexible steel wire or 3-inch manila, 30 fathoms.
2 heaving lines, 12-thread hemp, 25 fathoms.
2 speed cones.
1 set signal flags.
1 stadimeter.
2 megaphones.
1 Sweeping Manual, including sweeping signals.

EXTRA FOR MAINTENANCE

120 fathoms 3-inch manila.
120 fathoms 18-thread manila.
6 3/4-inch screw-pin shackles.
10 pounds marlin.
10 gallons linseed oil for wire upkeep.

DESCRIPTION OF GEAR.

EQUIPMENT.

23. Sweep wires are of high-grade flexible steel wire rope, 13/16 inch diameter, 2 1/2-inch circumference, 600 to 750 fathoms long. The same size wire is used with either the 12-foot or the 9-foot kite. A smaller wire, 1/2 inch diameter, 1 1/2 inches circumference, 300 to 500 fathoms length, may be used by small vessels for searching for mines, but it lacks strength and wearing qualities for sweeping mines clear.

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24. The reels or drums carrying the wire should be fitted with counters or other marks, to show how much sweep wire remains on the drum. For training purposes, the wire may be marked with bands of paint 6 inches broad, as in the following table; but in actual service these paint marks soon wear off, so that other means must be relied upon.

Length.
Color.
Distance apart.
Inches.
25 fathoms Green band
50 fathoms White band
75 fathoms Two green bands
3
100 fathoms Red band
125 fathoms Green band
150 fathoms White band
175 fathoms Two green bands
3
200 fathoms Two red bands
3

and so on - a green band at every 25 fathoms, a white band at every 50, two green bands at every 75, and red bands at the 100-fathom mark, equal in number to the number of hundreds of fathoms. In case a counter is connected to the winch drum, the above marking is not necessary.

25. Water kites are made in three sizes - 12-foot, 9-foot, and 6-foot. For mine-sweeping operations the 12-foot and 9-foot sizes are used with the 13/16-inch wire, the size of kite depending on the size and facility of the sweeper for kite handling, and on the speed. For 10 knots or over, the 12-foot size is used. For mine searching operations the 6-foot kite is used with the 1/2-inch wire, at speeds of 4 to 8 knots. This or lighter gear can not be depended on to do more than discover the presence and position of mines.

26. Kites consist of two long sides placed edge together at a right angle, and one short bottom piece, all made of wood suitably braced and secured. Two towing bolts are fitted on the upper edge or angle of the kite and are connected by a short chain bridle. There is a ring in this chain bridle, making two unequal legs. On this "kite ring" are two shackles. The forward one of these two shackles takes the kite wire, and to the other shackle is secured a kite pendant, which has at its outer end an eye and ring. Through this "kite pendant ring" reeves the sweep wire. The position of the two towing bolts on the kite has been determined by experiment, as has also the position of the kite ring in the chain bridle and the length of the kite pendant. The front end of the kite is stiffened, and the edges are cut away, so as to prevent the sides being forced in by the pressure of the water, and for protection in case the kite strikes the bottom.

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27. The greater the speed for a given length of kite wire out the deeper the kite will dive. If the kite wire is less than 30 fathoms in length it should be tailed with a 5-inch manila line for easing away. This arrangement spares the friction on the kite wire when hauling it in, does away with a winch drum for the kite wire, since any small drum will take the manila, and greatly facilitates the recovery of the kite. This is a fitting that can be left to the sweeping vessel to make. The kite wire reeves from the reel or drum of winch through fair leads on deck to roller chock at the stern to the kite, where it is shackled to the bridle ring. In sweepers fitted with shear legs or gallows frames heavy enough to take the strain of the kite wire while towing, the kite wire leads overboard through a block on the shearlegs, instead of through a stern or quarter chock.

28. When the kite is down the kite wire drum of the winch should always be connected with the engine. If not fitted with winch drums holding the kite wire, this wire must be secured to bitts while the kite is down.

KITE PENDANT.

29. Attached to the bridle ring is a short pendant called the kite pendant. At the outer end of the kite pendant is an eye in which is a steel kite pendant ring. Since the ring is cut or scored by the wear of the sweep wire in reeling in and paying out, a shackle is used to connect the ring to the eye of the pendant, to allow easy renewal of the ring; otherwise the grooves which are cut in the ring by the sweep wire will in turn cut the sweep wire.

SAFETY SHEARING GEAR.

30. For training purposes and for sweeping over rocky bottoms, or with sweeping winches which do not have brakes that render under sufficient strain to break the sweep wire, an automatic release is necessary to relieve sudden strains caused by the sweep fouling a rock or other immovable object in the bight. This release consists of a shearing pin of known shearing strength - 20,000 pounds - which connects the two parts of a shearing pin coupling. This coupling is inserted in the sweep wire so that it will remain abaft the kite ring of the slip boat.

31. A shearing-pin pendant of the same size wire as the sweep wire and 40 fathoms in length is secured at one end to the pelican-hook slip on the slip boat. From there it leads through the kite ring and fair-lead chocks and is tailed with the shearing-pin coupling, to which is shackled the end of the sweep wire passed over from the winch boat. As the boats open out to sweeping distance, the slack of the 40-fathom pendant is thrown over clear of the screw, thus preventing a sudden strain liable to shear the pin.

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32. When the shearing gear is not used, the end of the sweep wire is rove through kite ring and fair leads and secured directly in the pelican-hook clip.

33. The shearing-pin couplings are made of manganese bronze or of steel and consist of two parts, male and female, which fit accurately together, the pin completing the connection. Each casting is shaped to provide an eye, to which the wire is shackled or spliced.

BUOYS.

34. (a) Sweep buoys should have not less than 450 pounds buoyancy and, if used to hold up the bight of the sweep wire over rocky ground, should be spaced about 80 fathoms apart on the wire. They should be capable of withstanding pressures at a depth of 30 feet and be securely slung or shackled to the buoy pendants. The lower ends of these are connected to the sweep wire by shackles, which bring up against stops on the wire.

(b) Sweep buoys should be painted yellow.

(c) The use of buoys slows the operation of passing the sweep as the stops placed on the wire would be knocked off if the wire should run out at high speed. Hence the wire must be paid out slowly, necessitating a speed slower than usual in opening out. As the shackles are put on around the wire as it passes out, great care must be taken not to cut fingers, lose tools, etc. Buoys are put on by the winch boat. Buoys must all be put on before the kites are lowered.

35. Mark buoys, "Dan" type, are casks with an axial spar and counterweight, causing the spar to float vertically. The moorings consist of a 500-pound sinker and a 30-fathom mooring line of 1/2-inch flexible steel wire with eye and thimble spliced in each end. The buoy itself is equipped with a vertical bridle for mooring, with two thimble cringles, for attachment of the mooring lines for shoal and for deep water.

36. The following buoyage system is for use in United States waters only:

37. Lizards and slip ropes are used when the sweep wire leads overboard from amidships or from forward and are for the purpose of keeping the sweep clear of the propellers.

Channel buoys are spar or other form of buoys used to mark the swept channel. They must be of unmistakable type, large and seaworthy enough to be visible for at least 1 mile, and with strong and heavy enough moorings to remain in place under all conditions of weather for at least two weeks.

Mine-marker buoys are buoys to mark the position of a mine swept out of a channel or of a mine in channel that can not be moved.

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Buoyage system. - Buoys used by sweepers and mining vessels will be painted as follows:

(a) For marking the limits of mine fields, including the sides of swept channels: Red and white, in alternate broad, horizontal stripes. If the buoy is a cask or barrel the ends are to be red, with a broad white stripe between, in width about one-third the length of the cask or barrel, white stuff, red and white flag, diagonal halves.

(b) For marking an obstruction in the channel, including mines suspected to have been overridden by a sweep and to be still remaining: Spar buoy, red and black, in horizontal broad stripes.

(c) To mark where gear has been lost: White cask, with ship's name or initials, in black letters.

(d) For buoying sweep wire: Yellow.

(e) For buoying mines: Yellow.

(f) Permanent swept channels will in addition be marked near and at turns, by spar buoys, red on the starboard hand entering, black on the port hand entering, as usual in the United States Buoyage System.

INSTALLATION.

38. Fair lead rollers are of standard pattern for purposes of inter changeability and should be casehardened. Dimensions are 10 inches diameter extreme, score 2 inches deep, leaving 6 inches minimum diameter; height or width, 8 inches; pin, 2 inches diameter.

39. Gallows frame, shear legs, or inverted U frame may all be used to raise and lower kites of 12 or 9 feet length. Such frames have 6 1/2 feet clear lift above rail to throat of kite block when it plumbs the rail. The whole structure when properly designed will have the greatest spread consistent with the deck space available and be amply capable of withstanding the breaking strain of the wire used - 20 tons.

The use of buoys in sweeping is not obligatory, but they should always be at hand ready for use. It has been found that when the bottom is smooth the use of buoys can be reduced or eliminated.

A method of fastening buoy pennants to the sweep wire has been tried with success, as follows: Beckets to be spliced in the wire at the desired intervals and the ends of buoy pennants to be supplied with Coleman or topsail hooks instead of clamps or shackles.

40. Specifications for sweep winch for large sweepers. - General features. - Bedplate to be of solid casting, dimensions about 4 by 8 feet, to be bolted in place by through bolts; all parts to be as accessible as practicable for cleaning and oiling, of rugged construction to withstand rough usage in hands little experienced; the whole

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structure to be of strength sufficient for a stress exceeding the breaking strain of the sweep wire - 42,000 pounds.

Power. - The winches to be steam or motor driven, capable of hauling in the sweep wire against a strain of 20,000 pounds and of giving a drum speed of 600 feet per minute when reeling in against a strain of at least 3 tons.

Two drums, each large enough to carry 600 to 750 fathoms of 13/16-inch diameter wire rope; each drum capable of disconnection from power and holding or veering by a powerful brake, each drum capable of rotation by power in either direction.

Brakes on each drum to be controlled by hand (wheel), to hold against pull on the sweep wire up to 40,000 pounds, but capable of ready adjustment to hold against lesser strains, allowing the drum to give when the specified strain for which the brake is set up is exceeded.

Side drums or gypsies, one on each side, 18 inches diameter, locked to the driving shaft.

Levers and valves controlling the drums, engine, and brake to be within reach of one man, facing in the direction the wire leads out.

Steam piping to be well housed and lagged, and clear of operating valves and levers.

Sweep winch for small sweepers. - Same general features as for large sweepers, but for 1/2 or 9/16 inch diameter sweep wire. Drum speed to be the same, against a strain of 500 instead of 1,000 pounds. Strength of whole construction to be based on resisting the breaking strain of 9/16 inch flexible steel wire, or 26,000 pounds instead of 42,000 pounds.


CHAPTER IV.

STATIONS AND DUTIES.

41. There should be at least two officers on every sweeper; the captain, who must attend strictly to the conning of his ship, and an officer, or mate, in charge of sweeping operations on deck.

42. The captain should be assisted by a signal quartermaster and should be in communication by flag signals with other vessels and in communication with the sweeping operations on deck by megaphone, voice tube, or messenger.

43. The second officer stations the crew for the following duties:

(1) Provide all necessary gear and emergency repair material.
(2) Lead out and reeve off the sweep wire (on the winch boat) or the shearing-pin pendant (on the slip boat).
(3) Get out the kite ready for lowering, involving the reeving off and connecting up of the kite wire.

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(4) Station winchman.
(5) To receive or throw the heaving line.
(6) Inspect to see that all gear will fall clear.
(7) Lower the kite.
(8) Communication with captain.

SWEEPING PROCEDURE.

44. The following procedure is given as a guide for untrained sweepers:

Order: Prepare to sweep.
Signal: International "G" half way up.
On winch boat -
No. 1, tends winch, pays out sweep wire and kite wire for reeving off.
Nos. 2, 3, reeve off kite wire through fair leads and gallows frame, connect to kite with help of No. 1 at winch, rig kite out.
Nos. 4, 5, reeve off sweep wire through fair leads, through kite pendant ring, and back to the rail, where slack is stopped up and the end led out ready for passing by heaving line.

Note. - This procedure on the winch boat is modified on the slip boat, so that Nos. 4 and 5 lead out and reeve off the shearing pin pendant instead of the sweep wire. No. 4 secures the shearing-pin coupling to one end of the pendant and stops this end to the rail ready for shackling to it the end of the sweep wire when passed. No. 5 reeves the other end of the pendant through the kite pendant ring, thence through fair leads and secures the end to the pelican hook slip on deck.

The gear having been inspected for clear running and all hands stationed for passing the sweep, report is made to the captain, who then hoists international flag "B" halfway to the yardarm to show that he is ready.

Just before the signal to sweep is made the winch boat must be in station just astern of its slip boat.

45. Order: Sweep.
Signal: "G" all the way up.
Winch boat increases speed and ranges up alongside slip boat as close as safety will permit.
Boat to windward passes heaving line, which is immediately bent to end of sweep wire by Nos. 2 and 3 on winch boat.
Nos. 3, 4, and 5 on slip boat haul away on heaving line, bringing end of sweep wire up to No. 2. He shackles it to shearing pin coupling then unbends heaving line. Nos. 2, 3, 4, and 5 then throw pendant and gear clear. When no shearing-pin coupling is used, the slip end

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of the sweep wire is hauled to the pelican hook by 2, 3, 4, 5, hauling on the heaving line, or by a hook rope from the winch drum.

Meanwhile, on the winch boat, Nos. 4 and 5 are cutting stops along the side and keeping sweep wire clear of screw. Nos. 2 and 3 are tending kite to see that sweep wire falls clear of it. No. 1 is veering out sweep wire from the winch and checking it as necessary with the hand brake.

46. As soon as the slip boat has the sweep wire shackled to the coupling and the pendant has fallen clear astern, she hoists flag "B" all the way up and the winch boat opens out on the slip boat, veering wire as she goes. As soon as she has reached proper sweeping distance and is in position abeam of the slip boat she also hoists flag "B" all the way up and blows a short blast on the whistle, and then both boats lower kites.

No. 1 veers out on kite wire slowly as kite takes the water and dives.

Nos. 2 and 3 tend short guy lines to the kite to insure kite from twisting about and fouling the sweep wire before it takes the water.

Note. - Until boats become expert in thus passing the sweep, it is best not to open out too rapidly; but sufficient strain should be kept on the wire to keep it clear of the bottom.

47. (a) With special mine sweeping winches capable of paying out the wire rapidly and fitted with a powerful hand-wheel brake, the faster the better. Unless wire can be quickly veered and promptly braked, opening out too soon or fast may bring an undue strain on the wire, shearing the pin, or affecting the steering of the sweepers by dragging their sterns together.

(b) In paying out, be careful not to bring undue strain on the kite wire, either by sudden application of the brake, if veering from the winch reel or drum, or by suddenly tautening the inboard part, if reeving out around bitts or otherwise.

(c) A sudden strain will cause the kite to dive excessively, thereby causing danger of fouling the screws or breaking of gear by the kite striking the bottom.


CHAPTER V.

IN THE MINE FIELD.

48. Slipping the sweep. - The sweep should not be slipped unless it becomes foul of kites or mines which can not be cleared in any other way.

Before slipping, boats should close in on each other, winch boat heaving in, until the sweep wire is sighted. This is very important, as otherwise a mine that was not known to be on the wire may be left in or near the swept channel, unmarked.

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49. The signal to slip is six short blasts (- - - - - -) as a preparatory followed by one long blast (--). Upon this signal knock open the pelican hook and let the pendant, shearing pin coupling, and all go. Stop engines while hoisting kites on board to prevent fouling screw.

50. Mine in sweep. - A member of the crew specially trained should be stationed with his hand on the sweep wire to feel for mines picked up. The difference in vibration in the wire is easily recognizable by those trained to it. Be suspicious of mines if the sweep wire sings or if the engineer reports a drag on the engines (in light sweepers). Always have a buoy ready to drop if a mine is discovered.

51. Signal for "Mine in sweep" is made by firing a gun and, in American waters, hoisting International "C."

52. A mine having been discovered in the sweep, it should be immediately reported, brought to the surface and destroyed. The location of a mine field being indicated, other mines may be expected to appear.

53. The winch boat then proceeds to rapidly heave in and pay out about 50 fathoms of sweep wire at a time. This soon cuts the mine cable, especially if the serrated steel wire mentioned in reports from abroad is used, and allows the mine to come to the surface. Here it is either sunk by rifle fire or destroyed by gun fire.

54. If this procedure does not bring the mine to the surface, though the drag continues, it may be necessary to turn out of the formation with it and slip it in the nearest shallow water or at some place clear of the channel. In case it appears necessary to clear the mine from the sweep by slipping, the winch boat should steam ahead half a mile before reeling in to insure that the mine is not brought up on the sweep close to the ship. Buoy the spot where the mine is slipped.

55. If, after suspecting a mine in the sweep, the "singing" of the wire suddenly ceases and the drag is relieved, the sweep may have slipped over the mine. The spot should be reswept over.

56. When you find an unexpected mine, report the course on which you were sweeping. You may have been dragging it before it was discovered and the senior officer can then better judge what area to declare dangerous.

57. Sound when mines are found and again when slipping. This will insure shoaling or deepening mines to some extent.

GENERAL SWEEPING PRECAUTIONS.

58. Never maneuver over the water where you have just slipped. If clearing an area always turn toward the unswept water.

59. Do not sweep mines into your neighbor's water and leave them there. Overlap into his area to insure covering all water,

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then turn back and slip in a suitable place, but within your own limits.

60. Never carry sweeping operations beyond the zone declared by the senior officer of the base as dangerous, without informing him at once of the fact.

61. When slipping and heaving in, keep headway on so as not to drift into the position where your sweep was when you slipped.

62. Remember the effect of tide on the water you are covering, the state of tide at all times, the tidal, range, the strength of the tide and the corresponding dip of mines.

63. If in doubt as to whether you are dragging a mine or not, turn all sweepers once or twice without slipping and then continue to sweep or sight the sweep continuously.

64. Plot the position of all mines accurately on your chart.

65. If rocky bottom and shoal water reduce the distance between the winch boat and slip boat, shorten in the sweep wire or buoy the bight of the sweep.

66. If sweep parts and you can not account for it, go over the water again. If in doubt drop a dan buoy.

67. Take advantage of leading marks, ranges, and available fixes to keep the desired sweeping course. In a tide, the actual course steered may differ considerably from the course actually made good. In any case, sweepers should maintain position abeam of each other for the sake of uniformity.

68. Faithful, accurate station keeping and adherence to prescribed courses, more than all else, is insisted on as essential to reliable mine field clearing.

69. Report all mines discovered in accordance with the following table of characteristics:

1. Shape.
2. Number of horns.
3. Whether it has a central horn or not.
4. What kind of firing device, if no horns.
5. Color.
6. Appearance (as regards time in water).
7. Number painted on mine (if decipherable).

70. After a mine, once sighted, sinks without exploding, do not steam over the position until sufficient time has elapsed for it to have reached the bottom, as it may explode on hitting bottom.

71. If a mine becomes foul of the kite, buoy the kite wire, then cut or slip it and sweep up what you have done.

72. The appearance of a floating mine and also its number have proved the means on several occasions of recognizing the mine field from which it comes.

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73. Note in your navigational notebook the exact position in which you slip your sweeps on each occasion.

74. Keep a sharp lookout and plenty of headway on when heaving in the sweep, ready to veer instantly, as a mine may at any time suddenly appear foul of the sweep or kite wire.

75. Life belts are to be worn by all the crew when in suspicious waters. Kapok waistcoats are the best.

DESTROYING MINES.

76. Do not approach a moored mine which is watching unless in a very light-draft ship. There are probably others in the vicinity a few feet below the surface. Begin searching operations in the vicinity with small boats and light sweeping gear.

77. If mine has been brought up by the sweep and cut loose from its moorings, it may either be sunk by small arms fire or destroyed by gun fire, the latter being generally preferable as a mine which has been sunk but not exploded may later be exploded by some vessel dropping her anchor on it. Consequently mines should never be merely sunk where this event is likely to happen, such as over recognized anchorages, channels, etc.

78. Small arms must always be ready to sink a mine which has been cut loose either by own or a leading pair. The perforation of the mine case may be the means of only admitting water to destroy its buoyancy, or it may explode the mine by striking its firing mechanism, the chances being against this unless a "horn" on the mine is hit. British experience shows about 50 yards as the nearest a sweeper can be without suffering disabling damage from a mine detonated. Some vessels nearer than that have had their machinery disabled.

79. No mine should be fired at with small arms only to sink it from nearer than 50 yards, and none should ever be intentionally exploded nearer than 100 yards, and preferably two or three times that.

80. Most mines will explode when swept up in pairs or more by their own knocking together.

81. Mines found washing about in shoal water near the beach should be destroyed if possible without interfering with assigned sweeping, as the next tide may carry them out to sea again.

ALTERATION OF COURSE.

82. It is important that the course be changed as seldom as possible. The vessels of a sweeping pair must be mutually helpful in alterations of course and regulate their respective speeds to keep abeam of each other on the turn. Both boats should drop buoys at the beginning of the change of course.

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83. Courses set for sweeping had best be signaled in magnetic courses in points. Compasses marked in degrees are not yet common in vessels suitable for sweeping.

84. Temporary or emergency courses are signaled by whistle blasts, indicating number of points in the change of course, thus -

One long blast (--) followed by three toots (- - - ) signals a change of course of three points to the right.
Two long blasts (-- --) followed by two toots (- -) would indicate a change of course of two points to the left.

85. It is most important when turning that good station should be kept so as to make certain that the proper width of the channel has been swept at the point where the turn is made.

86. No turn should consist of more than 8 points. The pivot ship must take care in reducing speed not to go so slowly that the kite will be brought to the surface.

87. The area passed over in turning should never be considered as having been swept.

CHAPTER VI.

88. STANDARD SWEEPING CONDITIONS.

Speed. Interval apart. Sweep wire
to be veered.
Kite wire
to be veered.
Channel swept
by one unit.
Vessels
for unit.
Depth
of kites.
Size of kites and wire.
Knots. Yards. Fathoms. Fathoms. Yards. Fathoms.
Gunboats
12
400
1 400
11
300
6
6
12 feet.
2 1/2 inches circumference.
13/16 inch diameter.
Do
500
500
400
Tugs
9
400
325-400
11
300
6
6
9 feet.
2 1/2 inches circumference.
13/16 inch diameter.
Trawlers
Destroyers
10
300
300
8
300
6
6
9 feet.
2 1/2 inches circumference.
13/16 inch diameter.
Torpedo boat
10
300
275
12
300
6
6
6 feet.
1 1/2 inches circumference.
1/2 inch diameter.
Picket boats2 (50 feet).
7
150
2135
12
250
6
6
6 feet or wt., 1 1/2 inches circumference.

1 Can be reduced to 350 or even 325 fathoms if very accurate station is kept.

2150 fathoms may be required, depending on the accuracy of the station keeping.

Kite wire to be veered is measured from kite ring to water line of kite wire.

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CHAPTER VII.

GROUP SWEEPING.

Note. - Whenever it is mentioned below that sweepers turn out with mines in sweep, it is understood that they have not been able to saw them adrift from their moorings.

FORMATIONS.

89. As already stated, two sweepers constitute a "pair"; a collection of "pairs," a "group." Three pairs, and a leader vessel, seven in all, constitute a "standard group."

In sweeping a channel with a standard group, the pairs follow each other in various formations.

In a standard sweeper group, these pairs are known as the "leading pair," "center pair," and the "rear pair."

The formation for a standard group cruising ahead of the fleet is exact column, distance 300 yards.

90. There are three formations commonly used in group sweeping - column, starboard bow formation, and port bow formation. These are shown in Figures 4, 5, and 6.

91. In column sweeping formation, the slip boat of the leading pair is 250 yards directly astern of the guide. The winch boat is in position on the starboard beam of the slip boat. The distance between the winch boat and the slip boat is signaled; usually it is 350 to 400 yards, the same for all pairs in a group.

The slip boat of the center pair is 750 yards directly astern of the slip boat of the leading pair, and the slip boat of the rear pair is 750 yards directly astern of the slip boat of the center pair. (Fig. 3.)

The winch boats of the center and rear pairs are abeam of their corresponding slip boats and astern of the winch boat of the pair next ahead.

92. In starboard bow formation the slip boat of the leading pair is 250 yards directly astern of the guide. The winch boat is at the proper interval on the port beam of the slip boat.

The slip boat of the center pair is 750 yards behind the line of the leading pair and 100 yards inside of the winch boat of that pair, and the winch boat of the center pair is at the proper interval on the port beam of the slip boat.

The slip boat of the rear pair is 750 yards behind the line of the center pair and 100 yards inside the winch boat of that pair, and the winch boat of the rear pair is on the port beam of the slip boat. (Fig. 5.)

93. In port bow formation the distances, overlap, and intervals are the same as in starboard bow formation; but the line of the forma-

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Figure 3, showing mine sweepers in a column formation.

Fig. 3.

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Figure 4, showing mine sweepers in a column formation.

Fig. 4.

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Figure 5, showing mine sweepers in a starboard bow formation.

Fig. 5.

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Figure 6, showing mine sweepers in a port bow formation.

Fig. 6.

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tion runs on the port bows of the successive pairs, and the winch boats are on the starboard beam of their corresponding slip boats. (Fig. 6.)

94. Other formations that may be used are as designated and shown by sketches following:

Figure 7, showing mine sweepers in a line abreast formation.

Fig. 7.

95. "Line abreast (fig. 7)." -

Here the guide is either the second or the third vessel in the first line.

It is immaterial whether the second pair is on the left or the right of the first pair.

The winch boats of the leading pairs should usually be on the flanks.

The inboard boats of the leading pairs should be 200 to 250 yards apart, abeam of each other.

The third pair should follow at 750 yards distance, overlapping the other pairs by 75 to 100 yards each.

The safe width of the "fleet," or area swept over, in this formation is 900 to 950 yards.

The advantage of this formation lies in compactness. Signals are got through quicker and the boats kept in better control, especially in thickish weather.

96. Staggered formation (fig. 8). -

Guide right.

If guide left is signaled, the second pair is staggered to left of the leading pair.

This is a modification of "Line abreast."

The guide is right, in the sketch.

The second pair slip boat follows directly in wake of the guide boat, at about 750 yards distance; winch boat on starboard beam.

The third pair follows about 750 yards astern of the second pair, keeping the guide of the leading pair bearing about 7 1/2 degrees on the inboard bow.

The safe width swept in this formation is about 750 yards.

It is more suitable than "Line abreast" for narrow channels and for channels of variable width or with many or sharp bends, since the leading and second pairs may maneuver without crowding each other.

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Figure 9, showing mine sweepers in a staggered formation.

Fig. 9.

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FORMATION FOR SEARCHING.

97. Open line. -

Guide center.

The three pairs are in line abreast, with 150 to 250 yards interval between pairs.

Guide may be either left, right, or center. If guide is right, second and third pairs form successively on port beam of first pair.

This formation is not suitable for sweeping, but only for searching a suspected area. It is possible for one or two mines to be passed over undiscovered, but no more than that, unless the searching course made good should chance to be parallel to the line along which all the mines were planted.

In this formation an area about 1,500 yards wide may be searched by a group.

SWEEPING BY GROUP.

98. The senior officer of the group having made a signal to sweep and having signaled the course, speed, formation, distance between pairs, interval between the two vessels in a pair, the group takes the required preliminary formation, passes the sweeps, and commences sweeping.

99. If column sweeping formation has been signaled, the slip boats slow to one-third speed and indicate by signal that they are in position and ready to receive the sweep wire. The winch boats get into position 100 yards astern of their respective slip boats, make signal that they are ready to pass sweep, and reduce speed to one-third.

100. When all the sweepers have signals flying that they are ready for the sweeps to be passed, the signal of execution is made by the senior officer. The sweeps are then passed, vessels open out, kites are lowered, and sweeping proceeds, as described for a "pair."

101. If port or starboard bow formation is ordered, time must be allowed the pairs to get into position before signal is made to pass the sweeps. The procedure is then the same as for a single pair.

102. For indicating speed, the speed cones only will be used. All sweepers must be provided with them.

103. In order to indicate the channel swept its limits must be buoyed. This will be done by the sweepers as the area is swept over. The "rear pair" of a group is charged with the duty of marking the channel in case the formation is column. If it is a bow formation, the outboard boats of the leading and the rear pair plant the buoys.

104. Buoys will be dropped -

(a) Every mile as the channel is swept. They will also be dropped
(b) whenever the senior officer of the group signals to do so;
(c) whenever a pair turns out of the channel, by the pivot boat;
(d) whenever a countermarch is made, by both boats of the rear

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pair; (e) whenever a mine is caught in the sweep, by both boats of the pair finding the mine; (f) whenever course is changed, by the outboard boats or, in column, by the rear pair of a group.

105. The practice at first followed, of turning out as soon as a mine was caught in the sweep, has been largely abandoned. It lost much time, broke up the formation, and destroyed the certainty as to the area actually swept over, especially about the position where the mine was caught. Considering the difficulty and also the danger in that area, of re-forming the group to resume sweeping on the former course without leaving a holiday, especially in a strong current or seaway or without good marks, the advantage of standing on is clear, if it can be done in the circumstances. Turning out and leaving a mine, though marked, does not work out well in practice, since vessels may come upon these mines unawares and suffer damage. To give notice of all such marks would be impossible, even if their positions could be reported with sufficient accuracy.

106. A pair catching a mine in the sweep will therefore stand on as before, trying to saw the mine loose. The pair should keep its place in formation if possible, resuming standard conditions as soon as the mine is cut out or it becomes evident that it will stay on the sweep. The pair should not turn out unless there is favorable shoal to turn into, clear of any possible traffic; and then they should turn out only if other circumstances permit.

107. If it becomes necessary, however, for a pair to turn out with a mine, or to slip the sweep from some other cause, the following procedure should be observed:

PROCEDURE WHEN MINE IS CAUGHT IN A SWEEP.

108. When in column the pair finding the mine proceeds as described before, and the following pairs continue. When in bow formation the pair turns out as described. In case this is the center pair the following pair immediately sheers into the wake of the pair turning out, so as to overlap the leading pair, and thus close the gap left by the center pair. This narrows the channel.

109. Before slipping, the kites should be hauled up and the sweep wire then hove in, the two boats closing toward one another, until the sweep wire is sighted its whole length. If clear of mines, the slip boat lowers its kite again part way to a steady dive, then slips. If the slip goes before there is a straight-out lead to the kite, the slip end is liable to whip about and foul, damaging the kite.

110. The slip boat after slipping proceeds by the shortest practicable route to rear of the group, and stands by to resume sweeping as soon as a winch boat is available. In case it is impossible to proceed to the rear, slip boat lies to until the other pairs of the group

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have passed, and then takes the slip end from the first winch boat ready.

111. If it has been necessary to slip before the sweep was sighted, or if the shearing coupling parted, the winch boat, after the other boat has slipped, secures the sweep wire on the quarter or over the stern, hoists the kite and steams ahead one-half to three-quarters of a mile, then reels in sweep wire. Having reeled in, the winch boat proceeds by the shortest practicable route to rear of the group and when rigged again for sweeping passes the sweep to the first available slip boat. If it is impossible to go to the rear, lies to, clear of the approaching pairs, until the rear pair of the group has passed, and then starts sweeping with the first slip boat ready.

112. In the case of two out of three pairs of a group finding mines at the same time, it is not advisable for the one pair remaining to continue sweeping alone. This pair will stop, hoist kites, and if the sweep wire is buoyed, will leave it out. In a head tideway they may anchor to maintain position. The leeward boat should close in about 100 yards before anchoring, to prevent undue strain on the sweep wire when again getting underway. Anchoring at short stay should suffice, provided the following pairs are to come up soon.

REPORT OF AREA CLEAR.

113. When the group commander is satisfied that the channel is clear, he reports to his immediate superior "Channel clear." If there is any doubt as to whether the channel is clear, the sweeping should be done a second and even a third time. When no more are caught on sweeping it is almost safe to say that the channel is clear, though it is better to be on the safe side and sweep it again.

WHEN A SWEEP WIRE PARTS.

114. Should a sweep wire part, both vessels should immediately stop engines until the kite can be hoisted up and in; then both heave in the parted ends of the sweep, steaming ahead. If unable to keep ahead of the other pairs, the vessels of the broken pairs must sheer clear of the course of the following pairs.

115. As soon as possible they should pass the sweep again and rejoin the group formation. Properly equipped sweepers (two drum sweep winch) can best do this by the former slip boat becoming the winch boat, but without the two vessels changing sides, to do which would lose time unnecessarily. If the former winch boat were to pass her other wire as a sweep, she would have to cross the sweep wire and the kite wire, making liability to foul. This can be avoided and time saved by her taking the other boat's sweep (slip end). With practice, a pair will be able to exchange duties without changing sides easily, and still keep station in formation. In such case, the winch boat will be the guide of this pair.

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SPLICING A SWEEP.

116. To save time in resuming sweeping, when a sweep parts, the winch boat splices an eye in the end of the broken sweep wire, so as to have it ready to use as a kite wire, in case the other boat should part her sweep wire, too, on the next sweep. At the first opportunity the boat with broken sweep wire gets back the other part from the other boat, and splices the broken sweep, using a cut splice, which is quickly made and will not draw under heavy pull.

NOTES ON GROUP SWEEPING.

117. The senior officer of the group is responsible for the course steered by the group, and he should be in command of the guide vessel in a standard group. He should determine the course, intervals, bearings, speed, formations, etc., and should inform his group of all these factors before commencing to sweep, by written order if practicable, otherwise by signal.

118. The site on each or one side of the channel for slipping mines caught should be chosen beforehand. The requirements are that the water shall be shallow; as close to the war channel as convenient, in order to avoid having to tow the mines any great distance; and clear of all traffic.

119. The guide or leader vessel for the standard group should precede the group, flying the guide flag. The slip boats of the leading pair follows in the wake of the guide and becomes the guide of the group in case the group commander so determines. In this case his boat, the guide, takes any position desired, such as the slip boat, to make up a pair with any winch boat that has slipped. By having a flexible organization and with all boats fitted alike, any boat can be a winch boat or a slip boat, and in a standard group it is possible for the guide to pair up as a winch boat or slip boat, as may be necessary.

120. Whenever the pair having the guide finds a mine or has to turn out of formation, the winch boat of the next following pair becomes the guide and hoists the guide flag.

121. The formation for sweeping is determined by the width of the area to be swept. The width swept by pairs directly astern of each other would be sufficient for a channel for the fleet. The channel could be reported clear when the group had swept it until no more mines were reported on a sweeping. It would, however, be better to make another sweep with the group, if there be time, before reporting the channel clear.

122. In case the area is too wide for the pairs to cover by sweeping directly astern of each other, the formation should be the starboard or port bow formation. In this case the group commander must not only determine the course, speeds, etc., but he must also determine the numbers of pairs to use in one formation. This would depend

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on the width to he swept. The guides of the following pairs would overlap the pair ahead 75 to 100 yards.

123. If the total width of channel being swept by a group is diminished by reason of one pair of sweepers having to turn out with a mine in the sweep or because of the sweep carrying away, the boat in the next following pair, becoming the new outboard boat of the group, will commence dropping buoys so that the outer limits of the channel swept will always be marked.

124. The safe channel is about 50 yards inside of the buoys dropped by the outboard or flanking sweepers, since these buoys are dropped by the sweepers on the opposite side to that from which the sweep wire leads and since the sweep wire does not attain a sweeping depth until it reaches the water kite, somewhat inboard of the sweeper's track.

125. The signal to form for sweeping should be executed at least 1,500 yards away from the entrance to the channel to be swept, and the leading pair must get their sweep wire rigged promptly.

126. While taking position for "bow" formations, no attempt should be made to pass the sweep.

127. Tides and currents have a large effect on sweeping operations. When there is no tide or current, or when the tide or current is directly with or against the sweepers, the effect on keeping a straight channel will not need attention.

128. When the tide or current is across the channel to be swept, there are two cases to be considered:
(1) When leading marks are visible.
(2) When leading marks are not visible.

(a) Considering (1): The guide of each sweeping pair must keep exactly on the range, steering such a course as to do this. The winch boat must keep her station on the slip boat, at right angles to the range. The distances between following pairs must be kept. The leading ship of the fleet must make a course parallel to the range and pass through the middle of the channel.

(b) Considering (2): The guide of the leading pair estimates and allows for the tide as accurately as possible. The winch boat keeps station on her slip boat. The other pairs keep a line of bearing on the group guide parallel to the range. The fleet keeps in a line of bearing through the center of the channel.

129. In case a pair has turned out of the channel to slip a mine, the following pair should not turn out in the wake of the first pair should they catch a mine. To do so would expose them to the danger of running on the mine found by the first pair.

130. It is preferable to sweep against rather than with the current, especially if it is of a strength of over 2 knots. It is useless to sweep with a water kite which appears to be running shallow. Get it up and see if it is not foul on the sweep wire.

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131. Ships following sweepers through a swept channel must form on the line of bearing independently, being careful to keep on the line of bearing, not in the wake of the ship ahead. It is of assistance to the following ships in a cross tide or current if the leading ship of the fleet signals her heading as well as the course to be made good. When in pilotage waters with the sweepers out, the distance between ships of the fleet should not be less than 600 yards.

Figure 10, showing the first position of the mark boats.

Fig. 10.

USE, DUTIES, AND PLACING OF MARK BOATS.

132. Mark boats will receive orders to anchor in a specified position.

They will be supplied with a large mark flag, which is to be kept flying while at anchor. (This should be hauled down when shifting billet, but hoisted again when in the new position.)

The attached diagram illustrates what mark boats are required to do. A and B are the first position of the mark boats.

A dan buoy is always to be dropped by the mark boats in their original positions A and B. These buoys will mark the outer edge

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of the ground swept and will not be weighed until the day's sweeping is completed.

Note. - This diagram is drawn for sweepers sweeping on northeast and southwest courses. The two mark boats in this case will therefore be on a northeast and southwest bearing from each other.

133. Each time the sweepers pass the mark boat the senior officer of sweepers should give five short blasts on the whistle. Mark boats should then haul down their flag and shift to a position 100 yards on their own side of the outside sweeper, where they should drop a dan buoy. This position is marked H in the diagram for the mark boat A.

134. Mark boats should be able to fix this position and drop the dan buoy accurately if they shift promptly before the wake of the passing sweeper has died away. Mark boat should then keep underway close to this dan buoy and in swept water.

135. Directly sweepers return on reverse course and make five short blasts, the mark boat should then proceed and drop another dan buoy at a position 100 yards on their own side of the outside sweeper. This position is marked I in the diagram for mark boat A. The dan buoy H in the diagram should then be weighed and the mark boat should anchor alongside dan buoy marked I in the diagram and also weigh it.

136. The same procedure should be adopted each time the sweepers pass, but in the first case of sweepers passing mark boat marked B in the diagram it will only be necessary for this mark boat to anchor at position E in the diagram when the sweepers have passed.

137. When two pairs of sweepers are working, mark boats will shift into the same position with regard to the second pair as they did when only one pair was sweeping.

CHAPTER VIII.

KEEPING STATION ON A LINE OF BEARING.

138. When two or more pairs of sweepers are clearing a given area it is essential that the slip boats of each following pair should overlap the winch boat of the pair ahead. That will insure no unswept lane being left. This is a most important factor in mine sweeping, and no senior officer of a sweeping section is justified in declaring an area clear unless he has satisfied himself that the following rules have been adhered to:

139. When the tide is directly with or against the line of sweeping there will be, of course, no necessity to allow for it, but the strength and direction of the wind must be taken into consideration and allowed for.

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140. The guide or slip vessel of the leading pair of sweepers will signal the bearing (e. g., line of bearing N. 35 E. signal would be N. flag, 3 flag, 5 flag, E. flag) which indicates the line or direction or bearing that the sweepers must make good but not the course steered. Example: If mark boats were being used the line of bearing would be their bearing from one another. Sweeping at 400 yards interval and having no tide or wind to counteract, each slip boat following should place his ship and set his course so that he may follow in a straight line parallel to the track of the winch boat next ahead, keeping 750 yards astern and 100 yards inside. As mines generally come to the surface about the middle of the sweep wire, this is a safe position.

141. With the tide setting in a direction at right angles or obliquely to the sweeping track, it will be necessary to counteract its effect in a manner as shown hereafter.

Figure 11, showing the course steered against tide.

Fig. 11.

142. This must only be taken as approximate, owing to varying conditions, but it will serve the senior officer's purpose in establishing a tide allowance to be hoisted for the benefit of the slip boat following. They in their turn must not adhere strictly to it, but must pay more attention to the bearing previously hoisted, indicating the direction in which the sweepers wish to make good.

143. Instead, then, of acting as in the case of no tide or tide directly with or against, the slip boats will now keep an imaginary point 100 yards inside of the next winch boat ahead on the bearing hoisted by the guide boat. They must increase or decrease the tide allowance given as becomes necessary, according to the behavior of their particular vessels.

144. If the helmsman in each slip boat is given the bearing and the matter is explained to him, he may materially assist toward the object in view. The distance from the next pair ahead does not affect the method.

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Figure 12, showing three pairs sweeping with n tide or tide directly with, or against, line of bearing.

Fig. 12.

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145. With a strong tide setting across the track on line of bearing, it may have the effect of giving the sweepers the appearance of all sweeping the same ground, but this is not so, as the following diagrams will illustrate:

But owing to allowance for tide the sweepers appear superficially in formation to port. In reality, each slip boat is keeping her line of bearing east (true) on an imaginary point 100 yards inside the sweep of the winch boat of the pair ahead of him.

TO COUNTERACT THE EFFECT OF A KNOWN TIDE OR CURRENT.

146. From A, the position of the vessel as marked on the chart, draw a straight line A-B in the direction it is desired to make good.

From A toward C mark off with a pair of dividers the distance that the current would set in 30 minutes, 1 hour, or 2 hours, as desired, A-D. (Whether the distance A-D is for one-half hour, 1 hour, or any number of hours, it will make no difference to the course to be steered to counteract the effect of the current.)

Figure 13, showing how to counteract the effect of a tide.

Fig. 13.

With the distance that the vessel makes through the water in the same interval as that set for the current, as radius, and center A. strike an arc to cut the line AB, the course desired to be made good, The point of intersection in the case given below is E. Join DE. The direction DE is the course to steer to counteract the effect of the current A-C, and AE will be the course made good.

Sweepers at position A wish to sweep to position B but must counteract the effect of current setting in direction A-G at the rate of 2 knots. Vessel's sweeper speed, 6 knots.

Knots.
AE (speed of sweeper in one-half hour) 3
AD (drift of current in one-half hour) 1

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CHAPTER IX.

SWEEPER GROUP EVOLUTIONS.

147. For training purposes and until the Auxiliary Code Signal Book CB 229, used by mine sweepers and all auxiliary patrols in the British service, is placed in effect, the following will hold:

SIGNALS FOR SWEEPING.

148. Flag signals -

"G" half way up - Prepare to sweep.

"G" at yard arm - Form for sweeping, winch boats astern of slip boats, both ready for the sweeps to be passed.

"G" hauled down and pass sweeps, open out and sweep.

Four short whistle blasts. (Signal of execution.)

The senior slip boat will designate the sweeping formation as follows:

Guide flag at masthead. - Each pair sweep directly astern of the head pair.

Guide flag at port yardarm. - Port bow formation - Numeral hoisted will indicate number of pairs in formation.

Guide flag at starboard yardarm - Starboard bow formation. - Numeral hoisted will indicate number of pairs in formation:

"B" half way up - Slip boat is ready to receive sweep wire, or winch boat is ready to pass sweep wire.

"B" mastheaded - Slip boat has sweep on slip, or winch boat is ready to sweep or engaged in sweeping.

"C" mastheaded - Mine in sweep.

149. Sound signals. -

WHISTLE SIGNALS.

One long blast, turn to starboard.

Two long blasts, turn to port.

Add one short blast for each point of turn. Thus, one long, one short, means turn to starboard one point. The limit of one turn is four points. After turning four points, study for one to four minutes before turning farther.

Four short blasts, signal for execution.

Six short and one long, slip sweep wire.

One short, one long, one short blast, countermarch, each sweeper turning outboard 16 points.

Gun fired, mine in sweep.

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DETAIL SWEEPING.

150. The sequence of events in sweeping with a standard group, after the channel to be swept, formation, distance, and interval have been signaled, is as follows:

"PREPARE TO SWEEP."

1. "Guide" hoists "G" halfway.

2. All boats hoist "G" halfway in answer.

3. All boats get winch ready.

4. All boats rig kites.

5a. Slip boat hoists "G" halfway; sees kite, kite wire, kite pendant, pelican hook slip, ready in place; reeves heaving line through kite ring, ready to throw to winch boat; men ready at winch and along deck to receive sweep. Keep sharp lookout for signals.

5b. Winch boat hoists "G" halfway; sees sweep wire ready, about 25 fathoms rove through kite ring and then brought from aft forward, stopped along the rail; kite, kite wire, and pendant and winch ready.

"FORM FOR SWEEPING."

6. Guide hoists "G" to yardarm.

7. Guide reduces speed to one-third.

8a. Slip boat of leading pair takes station 250 yards astern of "Guide." Slip boats of center and rear pairs take station 750 yards and 1,500 yards astern of line of leading pair, directly astern if column sweeping is ordered, or on the quarter if "bow" formation is used.

8b. All winch boats take station 100 yards astern of their respective slip boats.

9a. Slip boats reduce speed to one-third, maintaining distance on guide.

9b. Winch boats reduce speed to one-third when in position.

10a. Slip boats hoists "B" halfway when in position and ready to receive sweep.

10b. Winch boats hoist "B" halfway when ready to pass sweep.

SWEEP.

11. Guide hauls down "G" and blows four blasts on whistle.

12. All boats haul down "G."

12a. All slip boats receive slip end and secure it.

12b. All Winch boats increase to two-thirds speed, come up on starboard (port) quarter of slip boats, and pass end of sweep wire to slip boat.

13. Slip boats masthead "B."

14. Winch boats put on buoys.

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15. Slip boats increase speed and open out to sweeping interval.

16. All boats lower kites.

17. Winch boats masthead "B."

18. Gun fired, by boat discovering mine.

19. Whistle signal change course 45°, by boat discovering mine. Winch boat or slip boat.

Note. - The turn is to the side designated beforehand.

20. Winch boat or slip boat discovering mine hoists "G."

21. Slip boat or winch boat repeats change of course signal as acknowledgment.

22. Both boats of pair put over channel-marking buoys.

23. Both boats turn out of channel.

24. The pair continues until mine has been dragged entirely clear of channel.

25. The winch boat throws over "mine-marker buoy."

SLIP.

26. Senior boat of pair makes signal to slip - six short blasts followed by one long blast.

27. Slip boat slips sweep at end of long blast.

28. Both boats haul down "B."

29. Both boats hoist kites.

30a. Slip boat proceeds to rear of column, preparing to sweep on way.

30b. Winch boat secures sweep wire over stern.

31. Winch boat steams ahead until certain sweep wire is clear of mine.

32. Winch boat reels in sweep wire.

33. Winch boat proceeds to rear of column, making preparations to pass sweep.

CHAPTER X.

SWEEPING - DEFINITIONS.

1. Slip boat. - The sweeper that receives the sweep wire; usually the senior boat and guide of pair.

2. Winch boat. - The sweeper that passes the sweep wire and unreels it from a drum on board, as the boat opens out to sweeping interval.

3. Bow formation (port). - Each following pair sees its leading pair on its port bow. The left of each following pair overlaps its leading pair about 100 yards. The sweeping group thus makes a diagonal formation across its course, the left leading.

4. Bow formation (starboard). - Each following pair sees its leading pair on its starboard bow. The right of each following pair overlaps

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its leading pair about 100 yards. The sweeping group thus makes a diagonal formation across its course, the right leading.

5. Clear channel. - Area swept over in wake of sweeping group (50 yards inside of line of buoys dropped by outboard sweepers).

6. Column (sweeping). - Each pair of sweepers following in wake of the preceding pair.

7. Distance. - Distance in yards between pairs of sweepers measures from the guide boat on one pair to the guide of the next ahead of next following.

8. Flank. - The right or left of a group of sweepers. The right or left side of the sweeping channel.

9. Fleet. - One sweeping to the front or rear in one trip without countermarching; also the area swept over by one continuous sweep.

10. Front. - Direction in which sweeping is proceeding.

11. Guide boat (in pair). - The sweeper that guides as to the course and speed of the pair. Usually on the side towards the group guide.

12. Guide (in a group). - The leading outboard vessel, if a sweeper; otherwise a special boat in advance of the advanced flank, guiding as to the course and speed of the group.

13. Interval. - Distance in yards between two sweepers of a pair when they are sweeping. The number of yards interval is about equal to the number of fathoms of sweep wire out under standard conditions. Thus, sweepers at 300 yards distance will have 300 fathoms of sweep wire out, approximately.

14. Mine fields. - (Types to be encountered.)
(a) Simple line naval defense.
(b) Double line naval defense.
(c) Multiple line naval defense. Three or more lines.
(d) The above lines parallel with or at an angle to sweeping channel.
(e) Single observation mines.
(f) Group observation mines.
(g) Shallow antisweeping mines.
(h) Single mines (any type), anchored.
(i) Compound mines (any type), anchored.
(j) Drifting mines, single.
(k) Drifting mines, tethered.

15. Obstructions. -
(a) Submarine drift net.
(b) Submarine trap or moored net, awash.
(c) Submarine trap or moored net, submerged.
(d) Submarine net with mines attached.
(e) Wire entanglement cable.
(f) Sunken vessels or stone barges.
(g) Heavy boom obstruction.
(h) Heavy chain obstruction.
(i) Immovable antisweeping moorings.

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16. Outboard boat. - A sweeper which is on the flank of a group in starboard or port bow formation. There are two, called, respectively, the "advanced outboard boat" (in the advanced pair) and the "rear outboard boat" in the last pair of the group. In case either the advanced pair or the last pair turns out of the formation, these designations automatically pass to the corresponding sweepers remaining in formation. Outboard boats may be designated as "X" boat and "Y" boat, respectively. One will be a slip boat and one a winch boat.

17. Pairs. -
Leading pair: Leading pair of sweepers.
Center pair: Pair between leading and rear pairs.
Rear pair: Last pair of sweepers.
Broken pair: A pair of sweepers turning out with mine or having their sweep carried away.
A pair in which the slip boat, on release by slipping, proceeds to join with an extra winch boat.

18. Port bow formation. - Same as bow formation, port.

19. Position. - On proper bearing and at proper distance and interval from guide in formation.

20. Preliminary formation. - In column slip boat 600 yards apart with each winch boat 100 yards astern of its corresponding slip boat.

21. Rear. - Astern of group when sweeping.

22. Speed. - Standard speed is that corresponding to the number of revolutions made while sweeping under standard conditions. The speed through the water is 1 1/2 knots, more or less, below that for the same revolutions, unencumbered. Two-thirds and one-third speed also refer to the propeller turns, not to the actual speed through the water.

23. Starboard bow formation. - Same as bow formation, starboard.

24. Sweep buoys. - Cask or metal buoys used for burying the sweep wire to keep bight off the bottom.

25. Sweeper. - Vessel employed in sweeping.

26. Sweeping channel. - Area designated to be swept.

27. Sweeping group. - Two or more sweeping pairs operating together. A standard group is three pairs.

28. Sweeping pair. - Two vessels equipped for sweeping by means of a sweep passed between them. A slip boat and a winch boat.

29. Turn. - Change of course of 20° or less to continue sweeping channel.

30. Turn out. - Two turns of 45° each out of channel, to drag mines clear and slip sweep.

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NORTH SEA PHRASEOLOGY.

Nip of the sweep. - The position where the sweep wire passes through the kite ring.

Dashpot. - A small cylinder containing glycerine or some similar substance which is exuded gradually by a small piston through a tiny aperture. This is a safety arrangement which holds a mine to its sinker and can be arranged to form a delay release.

Bottom sweep. - A wire sweep with two short lengths of chain utilized to tow on the bottom and so destroy mines which have not been released from their sinkers or mines that have been sunk without exploding.

Catenary. - The shape which the sweep wire takes up in the A sweep, i. e., roughly like a trawl gallows.

Communication channels. - Small channels swept through a large mine area and bouyed by dan buoys for the safe ingress and egress of the sweepers to their anchorage while engaged in clearing the mine field.

Winch boat. - The vessel whose sweep wire is in use.

Slip boat. - The vessel which has the end of the sweep wire secured to a slip.

A sweep. - The commonest form of sweep with a single wire between two vessels.

B sweep. - The French type of sweep for use with a single ship, now practically obsolete.

Kite ring. - A hardened steel ring attached to a short wire pendant on the slings of the kite through which the sweep wire passes.

Dynamometer. - An instrument for measuring the strain on the sweep wire while towing. It indicates parting of sweeps, sweep touching the bottom, but can not be trusted to indicate when mines are in the sweep. There are two kinds - Salter and Parkes - but they have been withdrawn in all ships except fleet sweepers.

Cod of the sweep. - The center of the bight of the sweep.

Sawing. - The action of drawing the sweep wire across the moorings of a mine to accentuate the cutting effect. It can be done by turning, one of the pair decreasing speed and then increasing again, or by veering and heaving in the sweep wire. Turning is, however, the most efficient method of producing this action.

Dan. - A buoy used for all purposes in connection with mine sweeping.

Dan colors. - Color of each flotilla of sweepers painted on the dan buoys so as to facilitate recognition.

Dumping bars. - Dan buoys laid to mark a dumping ground. They are fitted with a topmark in the shape of a St. Andrews cross formed by battons 2 feet in length.

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Live dan. - Dan buoy for which a course is being steered in a clearing sweep.

Dead dan. - Dan buoy ready to be weighed not being further required.

Serrated wire. - A special type of wire so made to increase the cutting power of that wire on a mooring.

Fifie boat. - Scotch motor drifters. A Scotch fishing lugger with auxiliary motor.

Drifting mine. - A mine which has broken adrift from its moorings and is floating on the surface at the mercy of the wind and tide.

Floating mine. - A mine which is not moored, but is floating beneath the surface controlled by hydrostatic valve and electrically.

Moored floating mine. - A moored mine awash.

Fishermans buff. - A bladder buoy inflated with air, sometimes called a pellet.

Delay release. - Any form of mechanical contrivance which serves to hold a mine to its sinker on the bottom.

Overlap. - The distance which all pairs of sweepers in any formation overlap the line of sweep of their next ahead. This is always most necessary, so as not to leave any water unswept.

Soluble plug. - A safety arrangement on a mine made of sal ammoniac, brown sugar, or other substance which is dissolved by salt water. Until the plug is dissolved the firing gear of the mine can not come into action.

Searching or exploratory sweep. - This is a sweep carried out on a broad front to endeavor to locate mines. Pairs of sweepers are usually two and a half cables apart. Thus 50 per cent of an area is reported "searched" 25 per cent only is actually swept.

Clearing sweep. - A careful sweep of a mined area using an overlap to insure accuracy. It requires the use of dan buoys or mark boats or both, and of the patent log and sounding machine when fixes by shore marks are not obtainable.

Dan anchor. - A small anchor specially provided for mooring dan buoys used in conjunction with three-fourths hundredweight sinkers.

Singing of the sweep wires. - A singing noise sometimes noticeable in slow sweepers when an obstruction is being towed in the sweep.

Dan cage. - A special cage used as a top mark or dan buoys which mark one side of a channel, flags being used on the other side.