2115. To accomplish deep submergence most expeditiously in order to avoid collission or detection by air screen, an exact knowledge of how the particular submarine reacts for the maneuver is required. A cardinal principle common to all types is that THE RUDDER MUST BE KEPT AMIDSHIPS. Best speed combined with angle down by the head varies with types and is determined by experience. Planeing effect by the deck, combined with the tendency of resistance of conning tower fairwater to hold the bow up, may cause a slower speed than maximum to be most effective. Too much angle will reduce propeller thrust if stern is brought too close to surface and will expose stern to ramming if in close quarters. Too much speed at periscope depth will create turbulence which will increase possibilities of detection from the air. When increasing depth rapidly by means of the negative tank, care must be exercised in blowing this tank after sufficient downward momentum has been obtained to prevent blowing air through its flood valves when avoiding air screens or patrols.

2116. The time required for rigging for diving from the surface cruising condition varies with different types. Normally, in order to provide for careful checking of each compartment, about twenty minutes should be allowed. Under war conditions, the submarine rigs for diving before leaving port and remains in that condition until her return. This permits day or night readiness for diving without standby orders. Interior organization must provide for maintenance of integrity of this condition, or immediate restoration of it, upon sounding of diving alarm. Under these circumstances, it is good practice to have the ship rechecked at the beginning of each watch by the officer coming on watch.

2117. As standard procedure, each compartment should be provided with a check off list for rigging for diving. In the interests of safety, the interior organization should provide for checking each item by an officer, without trusting to memory, before the compartment is reported rigged to the diving officer. The checkoff system should provide for exercising care that nothing in the superstructure stowage may come adrift and reveal presence during depth charge attack.

2118. When running below periscope depth, it is standard practice to maintain at least 60 feet over the A frames. Sound equipment is manned at all times and particularly careful use must be made of it prior to returning to periscope depth from deep submergence. If circumstances warrant and permit, especially in unfavorable water for reliable sound reception, a turn through 90° at slow speed should be made while listening carefully on all bearings. The transition period in coming to periscope depth must be accomplished quickly and with sufficient speed to maintain control and preclude possibilities of broaching. The lower conning tower hatch should at least be tended and under uncertain conditions, it and all watertight doors should be closed. All inboard valves and flappers and antenna trunk and bulkhead flappers should be closed in these circumstances. For peace-time operations or for recognition purposes in war time, use submerged signal gun as prescribed in other instructions. Upon arrival at periscope depth, a quick periscope observation is made through 360° in low power followed by more careful observations, duration and care of which are dependent upon circumstances.

2119. All depth gauges should not be cut into sea pressure at one time. when shallow gauges are in use, deep gauges should be cut out. This procedure reduces the possibilities of having all gauges rendered useless by a close depth charge or bomb.

2201. During peace-time when on the surface submarines are operated in accordance with the General Signal Book and General Tactical Instructions.

2202. Most surface operations of submarines during wartime may be expected to be independent or in open formations not particularly vulnerable to aircraft attack and from which submergence of all units may be effected. Deployment on line of bearing is most suitable for this purpose, but quandrantal or hexagonal deployments may be used. Chapter IV, Section 10 contains information on deployment.

2203. At all times at sea, under wartime operating conditions, the submarine must maintain the following conditions of readiness:

      1. Readiness for quick dive at all times, which requires a sufficiently advanced stage of training that this can be accomplished by the section on watch.

      2. Guns and ammunition, including machine guns, for anti-aircraft defense in the most advanced stage of readiness compatible with their preservation and readiness for quick dive.

      3. All torpedo tubes loaded with torpedoes ready to fire and with one complete set ready for reload without further adjustments.

      4. Readiness to fire torpedoes from the bridge, particularly during night and reduced visibility.

      5. Bow planes kept rigged in.

      6. Steering and engine control habitually from the conning tower or control room.

      7. Main storage battery kept venting inboard (or into main induction on vessels so fitted).

      8. The mast and periscopes habitually maintained in the housed position unless raised for short periods for particular purposes, in which case they should be housed as soon as reasons for raising them no longer exist.

      9. Have superstructure free of gear. Deck gratings and superstructure access openings should be locked closed and tap welded to prevent accidental opening.

      10. Sources of oil slicks and air bubble wakes eliminated before proceeding on a war mission. Serious defects in this respect can be ascertained by looking through eye ports and through own periscope at slow speed. If conditions permit, submarines shall be inspected from the air while submerged to periscope depth in the vicinity of the base before proceeding on a war mission. This is particularly important after extensive overhaul or after taking on reserve fuel. If such defects are not eliminated, the submarine is not ready for a war mission. Attention at all times must be given the external tightness of oil tanks and outboard oil fittings (such as filling and vent connections) and to the external tightness of all outboard air lines and connections. Care must be exercised not to foul (with oil from bilges) the line used for pumping water from variable tanks.

      11. Whenever a reserve fuel tank is emptied, it is maintained full of its compensating water and flood valves not opened to sea until an opportunity is presented for flushing it out several times under conditions which will minimize possibilities of detection or of permitting residual oil in the vent lines to become well spread through the superstructure. Flushing is done normally at night and away from where it is expected the following day's submerged operations will be conducted. Lines, canvas, etc., are not stowed in the vicinity of vents for reserve fuel tanks in order to minimize possibilities of oil slicks from these sources.

12. At all times when on the surface, sufficient way is kept on the ship to permit quick diving or maneuvering to avoid being rammed, or maneuvering to fire torpedoes without delay in case a suitable target approaches. Immediate submergence is required in order to avoid bombing, gun or torpedo attack on own vessel if contact is made close aboard.

13. All operations, whether surface or submerged, are conducted as silently as possible in the vicinity of enemy surface or submarine craft when noise from exhaust, auxiliaries, etc., creates possible sources of detection.

14. Rigid economy of auxiliary power is in order whether on the surface or submerged.

15. Recognition signals shall be made known to, and passed on, by all bridge personnel. Recognition devices and signalling equipment shall be on hand. Recognition flares, when provided, should be kept ready at all times for identification of submarine to aircraft.

2204. 1. The ability of submarines to escape detection and make successful attacks at night depends to a large degree on the efficiency of the lookouts. Every effort shall be made to pick the best men possible for this duty and their training shall be carefully supervised. Lookouts of proven vision equipped with binoculars shall be stationed in accordance with existing instructions. All bridge personnel shall be tested for night vision and none showing unsatisfactory night vision shall be so employed.

      2. For submarine operations, each lookout shall be a combined horizon, surface, and sky lookout. S-class submarines shall have a minimum of one lookout. Lookout station is the bridge. Fleet submarines shall have a minimum of three lookouts. Lookout station may be the signal platform above the bridge or on the bridge.

      3. Rotate lookouts in order that no man has more than 45 minutes consecutively on lookout watch. Stagger the reliefs in order that only one lookout is relieved at a time.

      4. At night all lookouts shall be properly dark adapted, by wearing red goggles, before relieving.

      5. When a submarine is on patrol station and has a choice as to what course to steer, much can be done to improve the efficiency of lookouts by adjusting course and speed so that they are not blinded by wind and spray. On moonlight nights, the choice should be a course towards the moon, or away from moon.

2301. Sound equipment is manned at all times when submerged; and, if keel mounted, it is manned during reduced visibility, when on the surface, when speed permits and when contact with any craft (friendly or enemy) is possible.

2302. Enemy target propeller turn counts are taken whenever possible and are of valuable assistance in estimating target speeds. These should never be used conclusively and must not be used to supplant plotting or other methods of determining target speed for use in solving the torpedo problem. Changes of speed are readily detected by propeller count.

2303. Echo ranging during the conduct of an approach must be used with discretion and with full consideration of many factors. If it is certain that enemy craft lack the equipment necessary to detect transmission from own equipment on the frequencies used, it can then be used with impunity. Under these conditions, when approaching an unscreened target, echo ranging can no doubt be used effectively for checking course and speed, for solution of the torpedo problem, and for own maneuvers in conducting the final stages of the approach. The importance of obtaining a single ping range at about 2500-3000 yards in order to accurately determine target masthead height with which to correct speed data is obvious. Under these same conditions, periscope observations are usually available, but when the masthead height of the target has to be estimated, echo ranges may be more accurate than periscope ranges. If the target is surrounded by a screen, the problem of ranges through wakes left by screens will be difficult. The results must be evaluated before they are used conclusively if a valuable target has made herself subject to attack.

2304. Echo ranging by a submarine during an approach always presents the possibility of acting as an alarm to the enemy. An enemy vessel that hears the echo-ranging signal from a submarine may be able to maneuver to avoid attack. Conditions during the approach may make it highly probable that a periscope, when exposed, will be sighted by the enemy or that the enemy air patrol or screening vessels may force the submarine below periscope depth. Under these conditions, the advantage of using echo ranging to obtain an accurate range of the target during the final stages of the approach is unquestioned. In order to detect any underwater transmissions made by the submarine, the enemy must possess supersonic receivers tuned approximately to the frequency used, but not necessarily trained directly on the bearing of the submarine. Factors affecting the probability of the enemy detecting any echo-ranging signals are:

      1. Speed -- The efficiency of supersonic receivers decreases rapidly as speed is increased above 15 knots.

      2. The efficiency of enemy operations. -- Even well-trained listeners will become inefficient from fatigue after the equipment has been in continuous operation for several days.

      3. The strength of the supersonic transmission which is primarily dependent on the range.

      4. The condition of the water as affecting the transmission of sound in water. If echo ranging is resorted to, the submarine should make the least number of transmission possible and then only in the latter stages of the approach. Through training, it is possible that under favorable circumstances, a good sound operator can use bearings of the target's propellers to train the projector accurately on the hull so as to obtain an echo range with only one or two "pings'. If echo ranging is not attempted until ready for the final setup of the problem immediately before firing, the intelligence gained by enemy interception of the signal possibly may not be acted upon in sufficient time to affect materially the success of the attack.

2305. Uses of echo-ranging equipment installed in submarine other than during approach and attack include:

      1. Rapid communications that are directional and limited in range.

      2. Identification signals while on the surface during reduced visibility and when submerged.

      3. Navigation when approaching an enemy coast during reduced visibility, particularly when it is known that navigational aids have been removed or extinguished.

      4. Location of unwatched mine fields or submarine nets. Peacetime uses of the apparatus during reduced visibility include:

         1. Station keeping in formation.

         2. Locating and tracking passing vessels.

         3. Locating icebergs and

         4. Piloting near the coast when entering channels or uncertain waters.

         Another peace time use is for search and communications in connection with rescue and salvage.

2306. To realize the capabilities of echo-ranging equipment for torpedo approach, it is important that the personnel concerned be properly trained and indoctrinated raining must include coordination between the sound operators and the conning officer. The conning officer should be sufficiently conversant with the operation of the equipment in order that he may be capable of properly evaluating information obtained by the sound operator. Results of submarine echo ranging equipment in practice torpedo approaches are without doubt minimized by the majority of targets possessing similar equipment, by the mental alertness of the sound operators in the targets during these brief exercises, and by the confinement to an area as imposed by the problem. These artificial features are of value in providing strict conditions for submarine supersonic training, but should not influence any estimation concerning the true worth of echo-ranging equipment under war conditions. It is the best equipment currently available for its designed purpose and every possibility of its submarine application must be exhausted before its use is condemned.

2307. Training of sound operators must be continuous to obtain best results. Ample opportunities are presented during all submarine operations underway. Of particular value to the listeners is experience gained during approaches, tactical exercises, and fleet problems.

      During these occasions, sound training for all listeners includes:

      1. Taking accurate bearings of target's propellers.

      2. Tracking of target and (in submarine with two projectors) screening vessels.

      3. Estimating propeller revolutions per minute.

      4. Identifying type of target by listening to propellers.

      5. Obtaining accurate echo ranges with only one or two "pings" after bearing of target has been found.

      6. Distinguishing any changes by the target in course or speed.

      7. Estimating ranges of target through intensity of sound received or from character or quality of propeller sounds alone.

      If training in this latter procedure brings forth a solution to obtaining ranges by listening only, then echo ranging with its attendant dangers of enemy interception may be dispensed with during torpedo attacks. Two possible methods of estimating ranges through listening only should be developed: -- first, by audible means, operators should endeavor to estimate ranges through changes in sound intensity or from the character of propeller sounds to be verified by periscope observation when feasible so as to give operators necessary experience and also to check on accuracy; second, by utilizing electrical

means of measuring changes in sound intensity, using the decible meter. Readings of the decibel meter, plotted with accurate periscope ranges, will produce a range-decibel curve. Preliminary investigation indicates that at the beginning of an approach, it will be necessary to obtain an initial periscope (or supersonic) range at the instant the first intensity reading is taken in order to establish a point on the standard range-decibel graph which will give the slope of the curve for sound conditions existing during that particular run. Experience also indicates that intensity of propeller sound is affected by angle on the bow; however, it appears that for angles on the bow normally encountered during an approach (10° to 90°), this variation in intensity does not present an insuperable difficulty. It is hoped that standard range-decibel curves may be established in the near future.
2308. In addition to the use for approach purpose, one of the main wartime functions of all types of sound equipment will be for the purpose of determining of other craft in the vicinity of the target are clear of the approach and attack when they cannot be seen and when limitations of periscope exposures do not permit periodic panoramic views. Intelligent use of sound equipment by well-trained personnel is an important factor in reducing the length and frequency of periscope exposures. Future developments should be with this essential point in view. If at any time it appears to the operating personnel that the equipment furnished by the technical bureaus is inadequate or unsuitably adapted to the needs of the submarine service, it must be remembered that experimental and development personnel cannot progress unless they are kept fully informed of the problem from the submarine end and that there is no closed season against such development within the submarine service itself.

2309. Radio watches submerged with the probable necessity for continuous watch on sound equipment during war patrols by one, or even two operators, require an adequately trained force of competent ratings, exclusive of radiomen, for effective sound work. Accordingly, every opportunity should be taken to discover and develop prospective sound operators. Progressive training should be given all men, regardless of rate, showing sufficient aptitude and ability in sound technique. Experience has proven,a s in gunnery, that after once attaining proficiency by extensive training, sound operators cannot be expected to retain their efficiency without further continuous training.

2401. Two types of radar are at present installed in submarines. Each is valuable for navigational purposes, as well as for their primary purposes. Every advantage of training personnel in radar material, maintenance and operation should be grasped. Either one or both radars are in continuous operation when the submarine is operating on the surface.

2402. In operating radars due consideration must be given to the possibilities of the SD radar signal being picked up by the enemy. Intermittent use of the SD for 5 seconds at irregular intervals of not more than one minute is considered to be fairly safe procedure. Radars require warming up before being put in operation.

2403. While searching with SJ use power training. When contact is made shift to hand training and develop the contact by obtaining range and bearing. Shift to lobe switching as soon as possible. In applying radar information use both the TDC and plot. When the contact is enemy, develop the contact for attack. Take full advantage of visibility conditions, going to radar depth, when necessary, to avoid detection; and then to periscope depth to deliver the attack when the visibility permits periscope observations. In reduced visibility the attack may be carried out undetected with the submarine on the surface. This is more desirable and more effective than a submerged attack as the submarine retains the advantage of mobility and high speed.

2404. While tracking with the SJ radar make frequent 360° sweeps for other targets. Use the P.P.I.

2405. Success in radar tracking demands excellent interior communications. Frequent drills are required to develop the required standards of communications between the bridge, conning tower and plot. Special emphasis should be given to the instruction of talkers.

2501. The duties of the officer of the deck as prescribed by Navy Regulations are supplemented as follows:

      1. Keep the number of persons on the bridge at a minimum, requiring "Permission to come on the bridge" or "Permission to relieve the _____", in each case.

      2. Allow only one relief lookout on the bridge at a time.

      3. Keep lookouts alert, covering their own sectors, making reports using the proper phraseology.

      4. Maintain the passageway to the hatch clear at all times.

      5. Keep loose gear off the bridge.

      6. The following rules in general apply on contacts:

         1. Dive for aircraft contacts (except in friendly patrolled waters).

         2. Turn toward a periscope forward of the beam and away from a periscope abaft the beam, going to flank speed in each case.

         3. Turn away from small craft.

         4. Turn toward a target, diving if necessary to avoid detection.

      7. In friendly waters have recognition signals at hand.

      8. Carry out the following routine:

         1. Blow all sanitary tanks about one hour before diving.

         2. Stow 20 mm guns about thirty minutes before diving.

         3. Carry out diving procedure as outlined in ship's organization.

         4. Run at depth and make periscope exposures as ordered by C.O.

         5. When landmarks are available, keep ship's position cut in.

         6. In making periscope observations first make a complete sweep in low power for aircraft and close surface targets. Follow this, if all clear, by a slow search in high power.

         7. When a target is sighted, start the approach immediately.

         8. At sunset "rig for red" below in all spaces forward of the forward engine room.

         9. Have lookouts equipped and standing by.

         10. Warm up SJ Radar.

         11. Carry out surfacing procedure as outlined in ship's organization.

         12. Start the evening routine after surfacing and after having received permission from the C.O. This normally consists of starting battery and air charges, pumping bilges, blowing sanitary tanks, dumping trash and garbage and rigging 20 mm guns.

2502. Keep the ship compensated at all times.

2503. The ship's organization should contain in detail instructions for all men on watch below decks.

2504. During daylight surface cruising keep one torpedo forward and one torpedo aft set to run at forty feet. (Reset to ten feet at night and alternate torpedoes which are set at forty feet). The O.O.D. shall at all items keep himself informed of condition of the tubes and those set at forty feet.

2505. Take full advantage of smooth weather, long periods of submergence, etc., for servicing torpedoes, overhauling and checking equipment, upkeep, greasing routine, etc.

2506. Even during long patrols, a smart ship will maintain high standards of cleanliness.

2507. The following are considered sound practice:

      1. When surfacing with high pressure in the boat, close the lower conning tower hatch. The upper hatch can be opened as soon as the bridge breaks clear and the bridge manned. When pressure is equalized by the low pressure blower, open the lower conning tower hatch.

      2. When cruising on the surface at too high a speed to have sound heads lowered, one sound gear flood valve can be left open and the sound gear manned to listen for "pingers". Pings are often picked up before sight contact is made.

      3. Operation of one distiller twelve out of each twenty-four hours should provide sufficient fresh water.

      4. Cut bridge watches short in bad weather.

      5. Don't neglect greasing top side fittings periodically.

      6. Don't fight it out on the surface with an armed enemy, unless you can stay out of the range of his guns.

      7. Demand perfection in all dives and in maintaining depth control.

      8. Take every precaution against taking heavy seas down the hatch. It is sure to cause a lot of damage and may put a great deal of valuable equipment out of commission. This precaution should especially be taken when surfacing in a heavy sea.

      9. Pay especial attention, on patrol, to the galley, the quality of food, the cleanliness of all compartments and the cleanliness of personnel.

      10. Require a smart, alert watch at all times.

      11. When using the SD radar in enemy waters, turn on and off at irregular intervals, leaving it on 5 seconds and off 40 to 70 seconds.

      12. Check the T.D.C. Daily by running a check problem.

16 February 2006