Rear Admiral Charles J. Badger, President, General Board of the United States Navy, to Secretary of the Navy Josephus Daniels
DEPARTMENT OF THE NAVY.
March 17, 1917.
From: Senior member present.
To: Secretary of the Navy.
Subject: Estimate of the situation as to system of patrol and sweeping best adapted for protection of shipping off port of New York.
Mission: To protect from submarine attack all shipping approaching or leaving New York.
1. According to shipping reports $1,000,000,000 is a conservative estimate of the value of shipping and cargoes entering and leaving New York monthly from and to foreign ports. In 12 months this is $12,000,000,000. One per cent of this is $120,000,000. Thus the money needed to provide protection to shipping against submarine operations off New York will be a very small percentage of the value of the property to be protected.
2. Enemy forces−Strength, disposition, probable intentions, etc.−The number of enemy submarines which may appear off the harbor is uncertain, but in view of the number supposed to be available, the distance they have to come, in groups of two or more, possibly accompanied by submarine tenders, but in any case the number will be small. As the object of the enemy is to destroy as much merchant shipping as possible in order to stop or reduce the shipment of supplies to the Entente Allies, attacks will primarily be made on merchant vessels.
3. To accomplish this the submarines will use torpedoes, guns, or mines.
4. Guns will be effective against unarmed shipping and be the most economical of the three weapons, because with a given weight of ammunition the return will be greater.
5. Torpedoes may be fired by submarines from the surface or submerged, but the number carried by a single submarine is limited, and therefore the range at which it will be profitable to fire torpedoes must be short, especially when the submarine is submerged. Torpedoes will be used against the largest ships, as such ships will present the largest target and may be destroyed by a single torpedo.
6. Mines can be used in water not over 50 fathoms in depth, and if used, will be laid in the most probable tracks to be followed by shipping and as near the focus of those tracks off port as possible. They may be laid from large submarine mine layers, and have been laid from neutral vessels fitted with secret compartments. A combination mine laying and supply submarine may be employed.
7. It is improbable that mines will be laid in the areas in which it is expected to employ submarines with torpedoes and guns. Consequently a combination mine laying-supply submarine may at first lay its mines as close in as possible, and then proceed to a determined rendezvous to supply the gun and torpedo type lying off shore. Presence of mines in an area before a port will indicate that such an area will not be a cruising ground for submarines using torpedoes and guns.
8. Our own forces−Strength, disposition, and courses open to us.−Destroyers, light cruisers, and gunboats are all we have available at present to use against submarines. There are not enough of these to meet the needs of the situation in general even if sufficient for a single port. It will be necessary to take over yachts, fishing vessels, and suitable commercial crafts to make up the numbers which will be needed. It remains, therefore, to determine approximately what those numbers will be and the armament and qualities they should possess.
9. To combat submarines and to deprive them of the advantages which the ability to submerge gives them:
(a) If they use the gun, guns of equal or greater power must be used against them.
(b) If they lay mines, waters where they can lay them, and which it may be necessary to use must be swept, and may be searched by aircraft.
(c) If they fire torpedoes when submerged by day or from the surface at night patrol of waters by surface craft or search by aircraft is necessary to locate and trap or force them to keep under the surface, and convoy of large vessels by small craft may also be necessary.
Aircraft should be used to assist in the patrol of the approach to New York or other ports as necessary. In addition to shore bases hydroavions might be employed as mobile bases for small aircraft.
(d) Steps must be taken to trap and destroy submarines when submerged. For this purpose trap nets may anchored, drift nets used, and bombs provided for destroying submarines. Such bombs will be towed and exploded from towing vessels or thrown overboard from surface or aircraft, and fitted with firing mechanism[s] set to explode at a determined depth.
10. As submarines may suddenly appear in any direction, and carry one or two guns of 3 to 4-inch caliber, all merchant vessels should be provided with batteries of four guns (to obtain all around fire) of not less than 3-inch caliber, if practicable, but batteries of even six or three pounders will be of assistance to prevent submarines from closing in on the surface to short ranges.
11. Arming merchantmen gives them a measure of protection which goes with them throughout a voyage. The greatest menace to shipping from submarines at present is in the prescribed zone of European waters; vessels proceeding through such zones should be armed first. Trained gun pointer groups will be needed for all guns.
protection against mines.
12. While the menace from mines laid by enemy submarines on the United States coast is not believed to be great, provision should be made to meet it.
13. As New York harbor has been closed to submarines by nets placed at the Narrows, channels from that point to the lightships should be patrolled, and swept for mines if necessary. But as submarines can only enter these channels on the surface sweeping for mines outside the entrance channels to the 5-fathom curve will be the more important problem.
14. Due to distance which it is necessary to bring mines and the consequent limited number which will be available, the probability of repeated mine laying under the present circumstances, is remote. If resorted to at all they will be laid as close in as possible to increase the chance of their being effective and at the same time not interfere with submarines using torpedoes. Under these conditions the continuous sweeping of an area approximately 8 miles wide and 15 miles long outside the channel entrances would probably be a good indication of the presence or absence of mines in the approaches to New York.
15. Assuming a pair of sweepers covers 400 yards and can sweep at 5 knots, the above area would require 10 pairs, or 20 sweepers, working 12 hours a day, or to sweep daily and allowing half-time on station, a total of 40 sweepers.
16. If mines are found in the above area, sweeping should be extended off-shore, possibly as far as the 50-fathoms curve. Sweeping should continue until it is demonstrated that no mines are present. The most direct route to deep water will require the fewest number of sweepers.
17. Off-shore sweeping may consist in:
(a) Sweeping a wide band in which mines may be laid in depths of 50 fathoms or less.
(b) Groups of sweepers to precede vessels proceeding singly or in groups.
(c) Continuous sweeping of a lane of definite width.
18. By the first method the area off New York would be over 5,000 square miles, and even if the vessels required were available the benefits obtained are not sufficient to warrant the adoption of this method.
19. By the second method, vessels singly or in groups could be conducted on any desirable course but only at the speed of the sweeping vessels (5 knots), and if mines were found the convoy would have to stop until the area was cleared. With a limited number of sweepers the number of vessels in a convoy group would necessarily be large. The large groups, slow speed, and possible necessity of stopping, all favor the attack by submarines. As the shortest distance from Ambrose Channel to the 50-fathom curve is more than 80 miles, vessels preceded by sweepers could cross this area in one daylight and must follow the sweepers at night or deploy over a possibly mined area. Therefore this method is rejected.
20. By the third method, given a large number of sweepers, a lane 10 to 20 miles wide could be kept swept and merchant vessels could proceed without further assistance at best speed at any hour across the area.
21. Allowing a distance of 400 yards per pair of sweepers and a speed of 5 knots, a lane 10 miles wide and 80 miles long would require 100 vessels and 16 hours, and to sweep the lane once per day and hold vessels one-half time on station, would require 200 sweepers. By reducing the lane in width the number of sweepers will be required proportionately, but the narrow lane must be well defined, as by a line of buoys, so that vessels keep in the swept area. This has the disadvantage of indicating the route to the enemy, but alternate lines of buoys could be planted and the swept lanes shifted as deemed necessary.
22. The question then arises how wide a lane to sweep and what system would require the least number of sweepers.
23. Considering the question of a line of buoys spaced at 5 miles on a known bearing (say 130° from Ambrose Channel) merchant vessels should be able to keep within 1,000 yards of this line in average conditions of weather in daylight, outgoing vessels passing on one side (right) and incoming vessels on the other of the buoys. This will require a swept land on each side of buoys, but if vessels going in both directions are on same side of buoys the outer vessels are more liable to get too far from line buoys. The sweeping of this double lane can be done by:
(a) Assigning a group of sweepers to a section of so many miles.
(b) Sweepers proceeding out one side and in the other, groups to start from inner end at fixed intervals.
24. The latter method has the advantage that no vessels are required to proceed to distant station, but all are usefully employed as soon as they start from inner limit.
25. Furthermore, no time is lost in turning at end of sections, sweepers are always proceeding in same direction, as traffic and overtaking vessels need only pass to opposite land to pass a group of sweepers.
26. Reduced to a schedule this plan would work out as follows:
(a) Sweepers to work in groups of three pairs each; first and second pair to sweep in echelon, covering about 900 yards, and third pair to serve as guides and mine-destroying vessels, and to replace either of other pairs as necessary.
(b) Speed: Daylight (6 a. m. to 6 p. m.) 5 knots; night 2 1/2 knots.
(c) Group A leaves Ambrose Channel 6 a. m., first day; group B leaves Ambrose Channel noon, first day; group C leaves Ambrose Channel 6 p. m., first day; group D leaves Ambrose Channel 6 a. m., second day; group E leaves Ambrose Channel noon, second day; group F leaves Ambrose Channel 6 p. m., second day.
(d) Group A leave[s] outer limit at 6 a. m., second day and other groups at correspondingly later hours.
(e) All sweepers return to starting point at 6 a. m., noon, or 6 p. m., and can be relieved there as necessary, after one or more round trips, 48 hours being required for each round trip.
(f) Allowing for reasonable delays, a distance of 75 miles will be swept; groups of sweepers will be 25 miles apart and every part of the lane will be swept twice during each day and once during each night.
(g) The number of sweepers required as outlined above would be 36, and, allowing only half time on station, a total of 72.
(h) If this number of sweepers is not available, a proportionately shorter distance, or less width of land, could be swept by the same system, beginning at the inner end and extending as more sweepers become available.
27. The practicality of employing these vessels for sweeping as indicated is, however, problematical. Placing buoys to indicate a narrow land and so restrict the area to be swept introduces an objectionable feature, because they indicate the track shipping will follow and assist the enemy in both mine laying and torpedo operations. A system of sweeping narrow lanes offshore marked by buoys is therefore not recommended.
Protection Against Torpedoes.
28. If, under the circumstances, submarine operations are assumed to be practicable off New York, attack with torpedo seconded by the gun is more probable than by laying mines. Consequently, a protective patrol by armed surface craft should be maintained for the purpose of capturing, destroying, or driving submarines from the area patrolled. This surface patrol should be supplemented by aircraft.
29. The waters to be patrolled extend from the net obstruction at the Narrows to as far offshore as practicable with vessels available. For the part from the Narrows to the channel entrances, the smaller harbor craft can be used.
30. The vessels used for the outer patrol should have good safekeeping qualities and it is desirable that they be of not over 12 feet in draft. Speed to overtake a submarine on the surface is desirable, 18-20 knots.
31. With an unlimited number of vessels the entire area off New York should be patrolled, but with a limited number better results would be obtained by a more efficient patrol of a limited area, or land, such lane to be shifted as considered desirable.
32. Any method of protection by patrol vessels must follow the areas swept to the outer limits and then may extend in any desired direction.
33. Protection of vessels passing through danger zones may be effected by patrol vessels:
(a) By convoy of individual vessels.
(b) By continuous patrol of lanes, or areas, vessels to be protected to proceed through them at their maximum speeds.
(c) By a combination of these methods.
34. If convoy is adopted vessels should as far as possible be convoyed individually to avoid a mass formation and to present a target of minimum density.
35. During the month of January, 1917, 393 merchant vessels cleared from New York for foreign ports, and average of 13 per day, although some days this number was probably considerably exceeded. Allowing four patrol vessels for each vessel convoyed, 52 vessels would be required, and, assuming that an equal number of vessels enter, a total of 104 vessels for convoy would be needed daily. If the speed of the vessels convoyed averaged 12 knots, they would be protected for 100 to 150 miles offshore, and convoying vessels return with incoming vessels the following day.
36. The average number of vessels leaving daily for domestic ports is reported to be about 12. Under war conditions all vessels proceeding in and out would be subject to attack and it is probable that no attempt would be made to differentiate coastwise shipping bound for Europe. Therefore, if individual vessels were given protection an average of 200 patrol vessels would be required, without allowing for reliefs.
37. If the method of continuous patrol of lanes is adopted it could be maintained as follows:
(a) Assign individual vessels to a certain section or area.
(b) Have all vessels work in a circuit over the area to be patrolled.
(c) Combine methods (a) and (b).
38. The distance between patrol vessels will depend upon the distance of which periscopes can ordinarily be sighted.
39. If the above methods the first method of dividing the patrolled area into circuits or stations will permit the employment of vessels at distances from their bases proportionate with their endurance and the least seaworthy craft can be placed close to the port entrance.
40. Submarines will not attack single ships under way with torpedoes at a range greater than 1,000 yards, but assuming the maximum range at which the torpedo will be fired from the submarine at a single vessel at 2,000 yards, a lane at least 4,000 yards wide should be patrolled.
41. If the distance at which periscopes showing on the surface can be made out under average daylight conditions is 1,000 yards, then two lines of patrol vessels will cover a width of 4,000 yards and a patrolled limit of 100 miles will require 200 patrol vessels.
42. From the foregoing, it appears that for the average number of arrivals and departures from the port of New York the number of patrol vessels is approximately the same by the convoy method or the lane-patrol method. Necessary relief vessels would increase the numbers given above.
43. A combination of the two methods would consist in the patrol of such lanes as are more or less continuously swept and convoy beyond such lanes.
44. At night the efficiency of patrol is greatly decreased, therefore vessels should pass through closely patrolled area[s] or lanes lying in the immediate approaches to the port or be convoyed through them during daylight as far as possible. The sinking of the Laconia demonstrates the possibility of successful torpedo attack by submarines at night. Patrol vessels operating along lanes closely spaced will, in a measure, indicate by night or day the routes along which submarines will find their prey.
45. It is desirable that all patrol vessels have at least one 3-inch gun, but experience abroad shows that submarines do not operate on the surface in the presence of surface craft armed with a light battery. Lightly armed patrol craft, however, should be supported, if possible, by vessels with heavier batteries.
1. Arm merchant vessels as follows:
(a) Assign guns, first to vessels proceeding to European waters, and to other vessels according to liability of attack along the routes they are to follow.
(b) Batteries will consist of guns not over 5 or 6 inch caliber, nor less than 3-inch if available, and according as it is practicable to mount them.
(c) Mount at least one gun aft and one forward, but number, caliber, and location will depend upon numbers on hand, the practicability of mounting and working them, and the arc of the horizon which the guns will command.
(d) If guns of different calibers are mounted on the same ship, place the heaviest guns aft.
2. Establish sweeping operations as follows:
(a) Sweep entrance channels to New York as necessary and an area approximately 8 miles wide and 15 miles long southeasterly from the channel entrance. Forty sweepers will be required. This will require one-half sweepers to be on station at the same time. (See accompanying chart A.)
(b) Should mines be found in this area or should indications point to their being placed farther offshore, extend sweeping operations offshore, sweeping about 130° true, eventually to the 50-fathom curve, maintaining a lane at least 5 miles wide. Twenty-five pairs of sweepers could go over such a lane commencing beyond the above area in 14 to 16 hours. Patrol vessels will be necessary as guides and to assist in the destruction of mines if found. Discontinue this sweeping when this area is apparently clear of mines.
(c) The total number of sweepers required to meet above conditions and sweep to the 50-fathom curve will be 100, allowing one-half off station.
(d) Fit paravanes as practicable to bows of vessels as additional protection against mines.
3. Establish a patrol from the Ambrose Channel entrance as follows:
(a) Assign the patrol force in groups of three or four patrol vessels to convoy departing merchant vessels singly or in pairs approximately 100 miles offshore. Passage to be made through swept area and then over diverging routes as desired, and, as far as practicable, during daylight.
(b) The patrol vessels which have proceeded offshore will return with incoming merchant vessels and reverse the process followed when proceeding out.
(c) Limit of draft of patrol vessels to be not more than 12 feet, if possible. They should have a sustained speed of not less than 12 knots, a maximum of 18-20 knots is desirable, and their endurance under service conditions should be seven days, if possible, but not less than four days.
(d) Provide all patrol vessels with signal set, radio set, submarine microphone attachment, bombs, and paravanes for use against submarines.
(e) In addition to sweepers and convoy patrol vessels, organize a combined force of submarine hunters consisting of surface and aircraft. This force should consist of 50 patrol vessels and the necessary aircraft.
(f) For patrol duty provide 250 patrol vessels.
4. Offshore outer patrol:
(a) Organize an offshore or outer patrol to patrol routes beyond the positions where convoy of vessels ends outward or begins inward.
(b) Such patrol will consist of sea-keeping yachts, small gunboats, destroyers, suitable fishing or other craft. The routes patroled will diverge from or converge to positions where convoy ceases or begins, as may be desirable, and extend beyond those positions 100 to 150 miles.
(c) Provide 20 vessels for this purpose, one-half the vessels to be on station at one time.
(d) Lay down written instructions for systematic movement of these patrol vessels, which may be modified by radio; but use of radio by all patrol vessels to be limited as far as possible to reports of enemy movements for signals of distress.
5. The command of the patrol and sweeping force and control of the traffic to and from New York and its approaches shall be centered in one officer:
(a) He shall be furnished with information 24 hours in advance of the readiness of all vessels for leaving the port of New York. He will then arrange for their escort and will notify the agents or masters of the time they shall leave the lower bay.
(b) He shall also be given all information available of the sailing of ships bound for New York and the probable date of their arrival. These vessels are expected to pick up patrol vessels at or near the outer limit off the patrolled area and receive directions by word of mouth or signal (not radio) as to their further procedure.
6. Provide special radio code by which patrol vessels may receive or forward important information, but radio to be reserved for emergencies.
7. Cooperate with the Allies as to instructions to be given ships as to the methods of making passage and approaching port.