Axis Submarine Manual
Division of Naval Intelligence Identification and Characteristics Section
Diagrammatic View -- Italian 600-ton Submarine
In reply refer to initials and No. Op-16-F-20.
Serial No. 3849016.
OFFICE OF THE CHIEF OF NAVAL OPERATIONS
AXIS SUBMARINE MANUAL
- O.N.I. 220-M -- Axis Submarine Manual -- is designed primarily for the masters and seamen of our merchant marine and for armed guard crews. This publication is elementary in text and deliberately nontechnical. Its purpose is to acquaint seafaring men with some of the characteristics and tactics of the raider which approaches unseen and strikes without warning.
- There are included in this publication the principal types of Axis submarines. Vichy French submarines are included as well so that the coverage of the leading continental naval powers will be more complete. The techniques described are largely from what we know of German methods. However, it is believed that the principles discussed apply to the submarine forces of Italy and Japan, with due consideration for national traits -- caution and prudence in the case of Italy; reckless fanaticism in the case of Japan.
- As mentioned in the text that follows, the principal methods which are available to the master of a ship for thwarting his attacker are those of concealment and evasion. Thus, strict adherence to sailing instructions with regard to darkening ship, zigzagging, and similar precautions is clearly indicated. While these are negative means of defense they have positive and concrete results. Too often does the testimony of the survivors of a merchant ship state categorically that the lights were burning brightly or that the ship was not zigzagging.
- This publication is an unclassified public document. It its issued in quantity for the use of the merchant marine personnel of the United Nations, both officers and men. Wide and general distribution should be made of its contents so that those men who must run the gauntlet of a world-wide submarine blockade will know the nature of the enemy that seeks to destroy them.
Rear Admiral, U.S. Navy,
Director of Naval Intelligence.
Since the first World War, the German submarine has improved considerably. The modern U-boat is reported to be able to dive to depths in excess of 500 feet and to be impervious to depth charges which would have destroyed her forerunner of 1918. On the surface a submarine presents a small and tough target for gunfire. The rounded surfaces and the thick plating of the pressure hull render the submarine immune to damage from machine guns and other small caliber fire. The conning tower has a very thick plating and has a watertight hatch at its base. Even a penetrating hit on the conning tower will probably fail to destroy the submarine, and it may fail even to interfere with her continued operation.
German 517-Ton Submarine Captured by British
Damage to the upper part of the pressure hull of a submarine or to the control mechanism for diving prevents a submarine from submerging. If the submarine is unable to dive due to damage, and if she is far from her base and in waters controlled by the enemy, her eventual destruction by hostile air and surface ships is highly probable. A submarine confined to the surface, however, is not entirely defenseless. So long as the submarine retains her ability to use her guns and torpedoes, she is a dangerous vessel. It should be appreciated that not only are guns available to a submarine on the surface but torpedoes likewise can be fired from this as well as from the submerged positions.
517-Ton German Submarine
A submarine which is undamaged does not normally remain on the surface to use her guns against heavily armed ships or aircraft. By doing so she accepts a needless risk and loses the submarine's greatest asset, the ability to operate submerged and unseen. However, there are circumstances in which gunfire attacks will be made by the submarine. Gun shells are cheaper than torpedoes and there are more on board, as even the largest submarines carry only a limited number of torpedoes -- perhaps no more than 32. Also at night a submarine, because of her small silhouette, can approach a large ship and open fire before being seen. She may even destroy her prey before being forced to submerge.
The gun battery of the German submarine consists of 1 or 2 guns of 31/2 inches or larger caliber, which would be effective against unarmored ships at ranges up to 5 miles, and 2 machine guns which are for attacks close aboard and against exposed personnel. German torpedoes are of two types. one is an air-driven torpedo having an effective range of about 8 miles. The other is an electric and wakeless torpedo, which has a much shorter range of 2 miles. Both types of torpedoes can be fired when the submarine is either on the surface or submerged to periscope depth. Also, they can be fired on sound bearings with the submarine completely submerged to depths of greater than 100 feet.
One or two torpedo hits, if properly placed, will sink a large merchant vessel, although there are many instances of tankers and other ships which have come home after sustaining a torpedo attack from an enemy submarine (upper).
Submarines are equipped with very efficient under-water sound devices which permit them to discover the presence and bearings of large surface vessels within a range of 5 miles. This equipment also permits a submerged submarine to keep an accurate track of the position of attacking destroyers and other antisubmarine units. Evasive maneuvers are facilitated by the high maneuverability and the relatively small turning circle of the submarine. The German submarines are reputed to have made considerable progress in reducing the noise of their own machinery, and a submarine proceeding submerged at a speed of less than 3 knots is very difficult to pick up by even the best and most modern listening gear.
To destroy a modern submarine by means of depth charges the charge must be exploded very near the submarine's hull. To open up that hull a 100-pound depth charge must be exploded within 15 feet from the submarine. The lethal distance is somewhat greater with heavier charges, but in all cases in order to insure a kill the depth charge must be exploded close aboard.
Submarines can proceed on the surface at a speed of 18 knots or better. The submarine carries sufficient fuel to travel around the world. She also carries food and supplies for a cruise of several months' duration. Consequently, the German submarine operating along the American littoral does not need to be refueled or serviced by "mother ships."
There have been press reports that German submarines operating off the Atlantic seaboard have been refueled and have obtained supplies from disguised supply ships. While this is quite possible, the practice is much less general than is indicated by these press reports.
What definitely sends the submarine back home, if she is not sunk or damaged by her enemy, is the expenditure of her torpedoes. When the last bolt has been shot, she must return home to get a new supply. Torpedoes and the human factor determine the endurance of the submarine. This second fact, which may be easily overlooked by even seafaring men who are not accustomed to the cramped quarters of a submarine, is one of considerable important. Submarine crews are likely to be tough and courageous, but under the continual stress of war conditions, unless frequently relieved and given comparatively long periods of rest and relaxation, their morale may show signs of deterioration. The loss of several famous U-boat captains who were an inspiration to the entire German submarine service has, no doubt, had its effect on the less experienced commanders.
When running submerged, a submarine has a maximum speed of about 9 knots. Due to the rapid exhaustion of the storage batteries at this speed, it can be maintained for only an hour or two. At lowest speed, 2 or 3 knots, the submarine can continue to cruise submerged for as much as 2 days, traveling as much as 100 miles during that time. By spending part of the time resting of the bottom, the submarine can remain submerged for as much as 60 hours. Because of the inherent necessity for submarines to surface, preferably at night or in thick weather, to charge their batteries, it is imperative to maintain for a considerable time a close watch on the general area in which the submarine has been seen to dive. This is particularly true when the dive has occurred early int he day. At that time she has obviously less chance of evading her pursuers than when she may be saved by the near approach of nightfall. When it is safe to do so, submarines prefer to remain on the surface, keeping their batteries fully charged for submerged attacks or for submerged escape. To fully recharge an exhausted battery requires about 6 hours on the surface, but one-half of any battery deficiency can be made up in about 11/2 hours. Usually, therefore, a period of 1 hour on the surface is enough to recharge batteries sufficiently to permit cruising submerged at slow speed for 1 day.
In making a daylight torpedo attack on a merchant vessel, the submarine usually approaches submerged, exposing the periscope at frequent intervals, for only a few seconds at each observation. Normally, because of the slow submerged speed of the submarine, the approach upon her target will be made well forward of the merchant ship's beam. The greater the speed of the merchant ship, the farther forward the submarine must be in order to initiate a successful approach. Because the submarine must make frequent and accurate observations and be fine upon the bow in order to be assured of a successful attack, the tactics of zigzag were adopted. This evasive principle frequently thwarts the submarine's plans; and when a zigzag plan has been prescribed, it is highly important that it be followed scrupulously.
Attacks are also frequently made at midnight and 0400, since these are the night hours when watches are in the process of changing, or when the eyes of newly established watch personnel remain unaccustomed to darkness. Since a period of 40 minutes is required to adjust the eye to darkness, this contingency may be avoided by overlapping watch personnel so as to maintain men on lookout who have undergone this adjustment.
Even in good visibility the merchant ship has small chance of seeing the brief exposures of the submarine's periscope or of detecting the submarine by listening devices before the torpedo has been dispatched. If, however, the merchant ship is screened by escort vessels equipped with good listening devices, the submarine must either accept a greater risk of detection or must fire torpedoes at a greater range, and consequently, with a smaller chance of hitting.
It must be borne in mind that the surface speed of the submarine is greater than the speed of all but the fastest or merchant ships. So, by proceeding on the surface outside of gun range, or outside of the visibility range of the merchant vessels, the submarine can frequently redispose herself so as to gain the position ahead to initiate either a submerged approach during good visibility or a surface approach during the hours of darkness. Good air coverage or fast, wide ranging, escort vessels, however, will make it hazardous for the submarine to attempt to overhaul her prey in this fashion.
In making night torpedo attacks, the submarine usually approaches on the surface, relying upon its small silhouette to permit an unseen approach to a firing position. The superior surface speed of the submarine will enable it to maneuver so as to take advantage of any special visibility conditions, such as moonlight, lighter sections of the sky near the horizon, or the glow of shore lights.
In torpedo attacks, either by day or night, the explosion of the torpedo is often the first notice of the ship being attacked. When a torpedo explosion is observed, it may be assumed that the submarine will be within a radius of 5,000 yards of the vessel -- roughly on the beam and on the same side as the explosion. As pointed out above, the track of the torpedo is not always visible since many of the modern ones show little or no wake. When the submarine has launched her torpedoes from a shallow depth, the submarine may broach and the white swirl of her propellers become visible.
After firing her torpedoes the submarine ordinarily takes care to avoid exposing herself to gunfire from the damaged ship; remaining out of sight until her prey has foundered or taken such a list that her guns cannot be manned.
In rough weather the submarine will generally dive beam-on to the sea, altering her course if necessary to reach this position. Normally she will surface head-on to the sea. Submarines forced to dive on account of air or surface attacks may alter course after diving. Furthermore, in order to confuse her assailant, a submarine may make a radical change of course just before diving.
QUESTIONS AND ANSWERS
- WHAT ARE THE PRINCIPAL TYPES OF GERMAN SUBMARINES?
- Coastal and Training type, 250-300 tons, illustration ("3").
- Home operational type of 517 tons ("2").
- Ocean-going type of 740 tons ("1").
- Large minelaying type, 1,060 tons, similar to ("1").
- WHAT ARE THEIR GENERAL CHARACTERISTICS?
- Single hull. Length, 136 feet. Maximum speed: surface, 13; submerged, 7 knots. Torpedoes: three in bow tubes, 2 spare -- 21 inch. Gun: one .79" [20 mm] automatic. Three hundred ton type is fitted with saddle tanks. Complement: 23.
- Fitted with external "saddle" tanks each side of hull. Length, 206-220 feet. Maximum speed: surface, 16-18; submerged, 8 knots. Torpedoes: four bow and one stern in tubes, 4 spare -- 21 inch. Guns: one 3.5" forward, one .79" [20 mm] on bridge. Complement, 35.
- Double hull; thin outer casing extends almost to keel. Length, 244 feet. Maximum speed: surface, 18; submerged, 8 knots. Torpedoes: four bow and one stern in tubes, four or more spare -- 21 inch. Guns: one 4.1" and one (or two) 0.79" [20 mm]. Complement, 40.
- Comparatively few of this class are operating at present. Length, 275 feet. Speed: surface, 16; submerged, 7 knots. Guns: one 4.1" and two 0.79" [20 mm].
In addition the above Germany has seized some 14 submarines in occupied countries. Some of these may be used on operation.
Certain of the larger type of U-boats carry torpedoes outside the inner, i.e., the "pressure" hull. They can also increase the number, given above, of torpedoes inside the boat.
- WHAT IS THE APPEARANCE OF THE VARIOUS TYPES AND WHAT MEANS OF DISGUISE TO THEY ADOPT?
The general characteristics of all types is a long flush deck rising toward the bows. The stem is sloping. The saw-edged net-cutter at the bows, (see photos), has now been discarded by the Germans though certain of their U-boats may still retain it. Italian U-boats usually have net-cutters. Clearing lines extend from bows to bridge to stern.
There are many reports of the various colors and paint schemes of enemy submarines sighted by merchant marine personnel and other observers. It seems that there is no standardized technique employed. Bearing in mind, however, that the submarine commander is an individualist and usually an officer of considerable resource, it must be assumed that his ingenuity has extended to the point of improvising paints or other protective covering suitable to the area in which he is operating so that his vessel will assume a chameleonlike aspect as possible. On the whole, however, an over-all neutral tone that blends with the seascape is frequently used.
Very often the only proof of an object sighted being a submarine is that it unaccountably disappears. There has been one case during this war of a U-boat disguising herself with sails; a dummy funnel emitting smoke might also be used. There is also the possibility of a hunted U-boat firing a slow-speed torpedo, leaving a trace of oil, which may induce pursuers to follow a false scent.
- WHAT IS THE EXTREME RADIUS OF ACTION OF SUBMARINES AND HOW LONG DO THEY ACTUALLY REMAIN OUT?
The large minelayers probably have an endurance of 8,900 miles, while the 740-tonners and the 517-tonners could cover about 14,000 and 10,000 miles, respectively, without refueling if proceeding, for the whole passage, at economical speed.
Though the cruises of the two latter classes do not usually exceed 35 and 30 days, it is probable that the 740-tonners could remain away from base for 2 months, if not unduly harassed.
The 300-tonners can carry out short "ocean" cruises and their saddle tanks, some of which contain fuel, would give them a probable endurance of 4,000 miles at slow speed.
- WHAT ARE THEIR CRUISING SPEEDS?
In general, submarines will cruise at not more than 10 knots, and the coastal type will probably cruise at less than this speed.
- HOW LONG CAN A SUBMARINE RUN SUBMERGED?
At her maximum speed, only for a short time, from 1 to 2 hours at most, but at slow speed the can proceed for long periods, up to about 48 hours. Her batteries would then be exhausted.
In almost all cases, however, she would avoid running her batteries right down like this, and would come to the surface to recharge them before the expiration of the periods mentioned.
Fresh air also become a vital necessity. Though U-boats have air-purifiers, yet the original supply becomes very foul after about 30 hours. When the crew are working hard or moving about, as is the case when they are being hunted, they use up the oxygen very much more quickly than when diving normally or resting.
On service, submarines rarely remain submerged more than about 12 hours, and that only in very bad weather or when resting, or persistently chased.
- HOW FAR CAN A SUBMARINE GO SUBMERGED?
As a rule the limit may be taken as 75 miles, though some German submarines could go for over 100 miles in case of absolute necessity.
A diving U-boat, with battery fully charged, could only travel from 9 to 12 miles of proceeding at maximum speed.
- AT WHAT DEPTHS DO SUBMARINES USUALLY PROCEED WHEN SUBMERGED?
When carrying out an attack, they proceed at about periscope depth, that is, at the depth at which the fully extended periscope just reaches to the surface. This depth is about 35 to 40 feet.
When cruising, submerged submarines also usually keep at periscope depth, except in very heavy weather, when they go to over 100 feet, or when they are expecting attack with bombs or depth charges, when they may dive to 300 feet if the depth of water permits.
- WHAT IS THE MAXIMUM DEPTH TO WHICH SUBMARINES CAN DIVE?
Modern submarines are generally tested for a depth of 300 feet, but it is possible for some boats to dive to 500 feet without injury.
For lying on the bottom they do not ordinarily choose localities in which the depth exceeds 240 feet.
The pressure on a submerged object is equal to 41/2 pounds per square inch for every 10 feet of depth. The pressure hull is roughly cylindrical and immensely strong. In most submarines, however, when at a depth of over 300 feet, weak spots are likely to occur and cause leaks. hatches may buckle slightly; valves, glands and pipes through the hull are liable to leak at a great depth, particularly after damage by depth charge.
- HOW LONG DOES A SUBMARINE TAKE TO DIVE?
In an efficient boat, proceeding with both Diesel engines, periscope depth can be reached in 11/2 minutes from the order given to dive. If the boat is proceeding trimmed down (as is customary in patrol areas), the time taken will be only 20 to 40 seconds. When completely submerged a submarine can gain depth at 11/2 feet, increasing to 2 feet per second.
- WHAT ARE THE PRINCIPAL AREAS OF ACTIVITY IN HOME WATERS AND THE ATLANTIC?
Unless detailed for some special operation, all available ocean-going U-boats are employed against allied shipping, mainly on ocean routes.
The 250-tonners, though now used almost entirely for training duties, could operate in the North Sea and the Baltic. The 300-tonners could cover these two seas and penetrate a short distance into the Atlantic.
German ocean-going U-boats, now based mainly at Biscay ports, can cover the whole of the North Atlantic down to the Equator. In the autumn of 1941, they started to assist the Italians in the Mediterranean.
When employed on minelaying duties, they may be expected to choose shipping routes in comparatively shallow water. On completion they can still attack with a limited number of torpedoes or by gun-fire.
- BY WHAT ROUTES DO SUBMARINES LEAVE AND RETURN TO THE NORTH SEA?
They usually proceed north of the Faeroes, occasionally calling at a Norwegian port. This route is preferred to the passage through the English Channel.
Now that bases with repair facilities exist on the Biscay coast, the passage to and from Germany is seldom make except by newly-commissioned U-boats on their first patrol or those which require an extensive refit.
- CAN A ROUGH IDEA BE GIVEN OF THE NUMBER OF SUBMARINES OPERATING SIMULTANEOUSLY?
It has been assumed that about one-third of the small type and one-quarter of the larger types might be expected to be on patrol at any one time. This would, however, depend on whether some important operation in contemplated or in progress.
The actual number operating at any one time cannot be stated. Probably between one-quarter and one-third of the total number of commissioned U-boats are at sea simultaneously. Germany has a very big U-boat programme particularly of the 517-ton class.
- WHAT ARE THE TACTICS OF A SUBMARINE ATTACKING A MERCHANT SHIP BY DAY?
When attacking unescorted ships in open waters a U-boat will probably endeavor to reach a position well ahead, unseen and on the surface. From here she will gauge her target's mean course. She will then dive fine on the bow, choosing her position from the point of view of light and sea. She will attack at an angle of roughly 90° from the target's course, firing 1 or more torpedoes at a range of 1,000 yards, or less.
When a convoy has an escort the above method would be risky. It is unlikely that an attack would be made on a single ship with an efficient escort unless that ship is known to be of very great value; but a convoy, so escorted, would probably be shadowed, the U-boat proceeding on the surface hull-down. She would then choose her line of attack so as to avoid contact with the escort as far as possible and would dive at high speed on a closing course.
If possible a U-boat does not fire a torpedo at a single ship when she is more than 11/2 points abaft the target's beam .The most dangerous arc is from 60° to 120° from right ahead. When the presence of screening vessels or the target's zig-zag interfere with an attack, a U-boat may fire at a range of 1,500 yards and from a position up to 2 points abaft the beam. When attacking a convoy she might fire a "browning" shot, probably using a salvo of torpedoes, aimed at the convoy as a whole without singling out any particular ship, when the range may be over 4,000 yards.
- DO SUBMARINES WORK TOGETHER OR IN ANY FORMATION?
The patrol-billets are usually so spaced that U-boats have freedom of movement in their particular areas. On receiving, by wireless, information which has been procured from aircraft or other U-boats, they would leave their areas and endeavor to intercept a convoy.
- AT WHAT RANGE DO SUBMARINES FIRE THEIR TORPEDOES, AND WHAT IS THE SPEED OF THE TORPEDOES?
When attacking single ships, German submarines endeavor, if possible, to close to a range of 500 to 800 yards to fire a torpedo. When attacking a convoy, the fire, if possible, at ranges between 500 to 1,000 yards.
At these ranges the torpedo runs at 35 to 40 knots (depending on the type), i.e., it runs 500 yards in 22 to 26 seconds.
It may be expected that longer ranges will be accepted if the target is screened by A/S vessels.
- WHAT DO SUBMARINES DO AFTER AN ATTACK?
One cannot say for certain just what tactics will be adopted. If the target is unescorted they will, as a rule, remain at periscope depth to watch the result of their attack. If an escort is present they will do their utmost to avoid the screening vessels. When the attack has been made at close range it is quite possible that a U-boat may continue diving at high speed and try to remain under a convoy. Normally, however, she will will turn off her firing course, dive deep to about 250 feet and proceed at slow speed till the hunt has slackened.
- WHAT IS A SUBMARINE'S TURNING CIRCLE SUBMERGED, AND HOW LONG DOES SHE TAKE TO TURN?
About 350 yards for the larger types and 200 yards for the coastal types. When proceeding submerged at 4 knots a 517 ton submarine takes about 5 minutes to turn through 180°.
- WHAT DISTANCE WILL A SUBMARINE GO IN ONE MINUTE SUBMERGED?
At 7 knots the distance run would be 236 yards (1 knot equals about 34 yards per minute).
- HOW MUCH OF A PERISCOPE IS SHOWN IN ATTACK AND HOW OFTEN; AND AT WHAT DISTANCE CAN A PERISCOPE BE SEEN?
This depends largely on conditions of wind, sea, and light, the number and positions of escorts and whether the target is zig-zagging.
In bad weather a periscope is very hard to see, this is partly offset by the fact that the U-boat
has to raise a considerable length of periscope to obtain clear vision above the waves. When at long range, as much as 2 feet 6 inches of periscope may be raised to enable details and course of the target to be obtained. As the range decreases the U-boat would show less periscope and, toward the end of the attack, she would possibly only show 6 inches in calm weather.
In the early stages of an attack a U-boat need not raise her periscope more than once very 5 minutes and then only for 5 to 10 seconds at a time; when nearing the firing position she will raise it every 4 or 5 minutes for not more than 2 seconds at a time.
A periscope cannot as a rule be picked up at a distance of more than 2,000 yards, even with good glasses. If, however, a U-boat is known to be on a certain bearing and weather and light conditions are exceptional, it may be sighted up to 6,000 yards, with glasses.
- HAVE SUBMARINES MORE THAN ONE PERISCOPE?
Yes, all modern submarines have two, and a good many have three periscopes, but, as a rule, only one of these is used at a time. Only one is fitted for use against aircraft.
At the commencement of an attack a thick periscope with high magnification is used to enable details of the ship and her course to be noted; in the final stages a thin attack-periscope showing a very small "feather" is used.
- DO SUBMARINES OFTEN ATTACK AT NIGHT AND WHAT TACTICS DO THEY ADOPT?
The number of night attacks, particularly on convoys and stragglers, has now increased considerably. Often a night attack will be carried out on the surface, but the optical qualities of U-boats' periscopes are very good and can be used in twilight and bright moonlight.
In any attack at night a U-boat would be guided by such considerations as position of escort, direction of the moon, and the afterglow of sunset, etc.
She would note carefully the tactics of the escort and run in on an avoiding course at high speed, fire her torpedoes and turn away, remaining on the surface, unless pursued by a fast hunting vessel -- in this case she would dive deep and probably reduce to dead slow speed. If she were not hunted she might remain awash and reload her torpedo-tubes in readiness for another attack.
- WHAT ARE THE WEATHER LIMITS FOR SUBMARINE WORK?
The worst condition for submarine operations is a calm sea, and if, in addition, there is a long swell running, it become almost impossible for a submarine to attack unseen.
At the other extreme, if the sea is rough, a submarine will become unmanageable when near the surface. If it is possible for her to make her final approach on a course at right angles to the direction of the sea, she may attack successfully in worse weather; but, unless she is thus favourably situated, she will probably give up any attempt to operate near the surface and will dive deep until the weather moderates.
ITALIAN SUBMARINESItalian submarines vary extremely in their design, having numerous classes and types rather than employing standardization. Among the 12 submarines the Italians had prior to the war heavy losses have been suffered due to lack of personnel training and the resultant panic encountered. Recently it has been noticed that the conning towers of several Italian submarines have been abbreviated to resemble the German type (upper).
Classes Length Tonnage Armament Tubes CALVI 276'7" 1,331/1,965 2-4.7" 8-21" BALILLA 282' 1,368/1,874 1-4.7" 6-21" FIERAMOSCA 270'3" 1,340/1,788 1-4.7" 8-21" MARCELLO 239'6" 941/1,260 2-3.9" 8-21" ARCHIMEDE 231'4" 896/1,255 1-3.9" 8-21" SQUALO 229' 810/1,077 1-4" 8-21" SANTAROSA 229' 815/1,078 1-4" 8-21" SETTEMBRINI 226'9" 798/1,134 1-4" 8-21" PISANI 223'9" 791/1,040 1-4" 6-21" MAMELI 212'1" 816/994 1-4" -21" BRIN 231'4" 896/1,247 1-3.9" 8-21" MICCA 296'4" 1,371/1,883 2-4.7" 6-21"
FOCA 266'9" 1,109/1,533 1-3.9" 6-21"
2 mine chutes
CORRIDONI 234'7" 803/1,051 1-4" 4-21"
ARGO 206'8" 689/857 1-3.9" 6-21" ARGONAUTA 201'9" 599/778 1-4" 6-21" GEMMA 197'6" 620/853 1-3.9" 6-21" SIRENA 197'5" 591/787 1-3.9" 6-21"
Italian Submarine Classes
- IS NAVIGATION DIFFICULT IN A SUBMARINE?
It requires unremitting care, owing to the frequent alterations in course and speed necessary to avoid patrols, etc., and to the varying currents at different depths. In general, however, the navigation of German submarines has been very good.
- WHEN AND HOW DO MINE-LAYING SUBMARINES LAY THEIR MINES?
The mines are usually laid either at high or low water. In moderate depths high water is generally preferred, as giving greater depth for diving. In waters too shallow for diving, mines would be laid from the surface at night.
While laying their mines, these submarines can proceed either on the surface or submerged, as the mines are usually released from inside the boat.
The mines may be laid at close intervals, i.e., about 50 yards, and in groups, or they may be laid singly at very wide intervals, say, 800 yards.
The majority of mines laid by U-boats are magnetic and are ejected from torpedo tubes. It is known that one type is short enough to allow 3 mines to be carried in 1 tube. Thus a 740-ton U-boat could carry 18 mines in her tubes and probably another 20 or more as spare.
It is probable that the new 1,000 tonners will lay moored mines; the number carried is 48. They method of laying is not known.
Cases are known of submarines having followed up minesweepers and laid their mines in the channel which had just been swept.
- IN WHAT SOUNDINGS ARE THE MINES LAID?
In the North Sea and the Atlantic moored mines are usually laid in waters where the depth is between 7 and 80 fathoms. In tideless waters they could be laid at a considerably greater depth.
Magnetic mines would probably not be effective at a depth of more than 20 fathoms. they are usually laid in about 10 or 12 fathoms.
- WHAT COLORS ARE THE MINES PAINTED?
German moored mines have, up to date, been painted black, but some have shown patches of red where the black paint has washed away. Magnetic mines rest on the sea-bed and cannot be seen.
- DO SUBMARINES OFTEN LIE ON THE BOTTOM?
This depends on circumstances and the ideas of individual captains. They may lie on the bottom in bad weather if it is not rocky and there is no danger of bumping. They may also do so when being hunted by surface craft or when resting, but some captains prefer to keep underway going dead slow at a safe depth.
- ARE THE RESTING PLACES KNOWN?
In general, any place with a sandy or gravel bottom and a depth of less than about 45 fathoms is suitable for a submarine to rest on the bottom.
- CAN SUBMARINES REMAIN STOPPED WHEN SUBMERGED, WITHOUT LYING ON THE BOTTOM?
A well-trimmed boat may do so for about 15 minutes at a time by juggling with her periscope or alternately flooding and blowing her adjusting tanks. It is possible that German submarines are fitted with hydrostatic buoyancy control (as fitted in some Italian submarines) which enables them to keep a constant depth over considerable periods when stopped.
For longer periods it is only possible in localities where layers of different density occur in the water and where occasionally a boat may lie submerged almost indefinitely with all machinery stopped, resting on a layer of dense water. This is most marked in the Baltic, Kattegat, and Sea of Marmora, but similar layers exist in other areas such as the approaches to large rivers, especially after heavy rain.
- WHAT ARE THE TACTICS OF SUBMARINES WHEN HUNTED WITH HYDROPHONES OR OTHER LISTENING DEVICES?
If the submarine is in deep water at no great distance from where there are soundings of 300 feet or less, she may make for this position, in order to lie on the bottom, unless it is rocky or there is danger of damage from bumping. Lying on the bottom is, as a rule, the only means by which she can stop all machinery and render herself entirely inaudible to her pursuers. If, however, she keeps under way she will usually proceed dead slow (1 to 2 knots) and reduce all sounds to a minimum. It is also possible that she may lie stopped at a constant depth using the hydrostatic buoyancy control.
German submarines, during their trials, are tested by hydrophone when running submerged, in order to ascertain the most silent speed. This varies in different boats, but is usually very low.
- ARE SUBMARINES FITTED WITH HYDROPHONES?
Available information indicates that the Germans are adhering to the hydrophone method of detection in their submarines, the instruments having been greatly improved since the war. It is stated that at 5,000 yards range these instruments can locate a ship and also determine her propeller revolutions. Submarines need not stop in order to listen but get much better results when doing so. The distance at which they can hear the sound of propellers also varies greatly with the bearing and the state of the seas. They also use hydrophones when hunted themselves.
It is probable that U-boats are fitted with super-sonic detecting instruments known as "Periphons."
- IS IT NECESSARY FOR SUBMARINES TO GET THEIR MASTS UP IN ORDER TO TAKE IN WIRELESS MESSAGES?
No. The two jumping wires, which run from end to end of the boat passing over the conning tower and forming a protection against nets, hawsers and mines, are fitted with an auxiliary aerial; and the submarine is consequently able to intercept signals directly she comes to the surface.
- DO SUBMARINES CARRY A SEARCHLIGHT?
Yes, a good many of them carry a small portable searchlight, which can be mounted on the bridge, but is seldom used, being intended mainly for signalling purposes.
JAPANESE SUBMARINESJapanese submarines are primarily developments of German World War I U-boats. The range of types varies from the older RO coastal classes to the long-range I types, some of which may be equipped to carry a collapsible plane or midget submarine.
Classes Length Tonnage Armament Tubes I 6, 8 343'6"
1 float plane
I 5, 7 320' 1,955/2,500 1-5" 6-21"
1 float plane
I 1-4 320' 1,955/2,480 2-5'5" 6-21" I 68-75 331'5" 1,400 1-4"-4.7" 6-21" I 62-66 320-331' 1,635/2,100 1-4" 6-8-21" I 61 I 53-60 330' 1,635/2,100 1-4.7" 8-21" I 52 331' 1,390/2,000 1-4.7" 8-21" I 51 300' 1,390/2,000 1-4.7" 8-21" I 121-123 279'6" 1,142/1,470 1-5.5" 4-21"
RO 33-34 239'6" 700 Surf. 1-3" AA 4-21" RO 26-28 230'8" 746/1,000 1-3" AA 4-21" RO 30-32 243'6" pp 655/1,000 1-4.7" 4-21" RO 60-68 250' pp 988/1,300 1-3" AA 6-21" RO 57-59 230'8" 889 Surf. 1-3" AA 4-21" RO 51-56 230'7" 892/1,082 1-3" 6-18"
Japanese Submarine Classes
- ARE SUBMARINES ARMOURED?
As far as is known, German submarines have no armour protection, either on the conning-tower or elsewhere.
- WHAT IS THE EFFECT ON A SUBMARINE OF THE EXPLOSION OF DEPTH-CHARGES OR BOMBS IN HER VICINITY?
Completed authenticated instances of the following are on record:
- So serious a leak is caused that the boat sinks immediately.
- A leak is caused, say by a hatch being buckled, which cannot be kept under [control] with the pumps and forces the boat to come to the surface.
- A leak is caused in the external tanks, which may result in so large a loss of fuel oil as to necessitate the return of the boat to her base, or may cause her to leave an oil streak in the water.
- The periscope lenses are shaken or damaged, which may also necessitate the boat's return.
- The hydroplanes may be forced hard up or hard down, or rendered difficult to work, causing the boat to come to the surface or dive to a dangerous depth.
- If the explosion takes place immediately above or below the submarine, the same effect may be produced as in (e) by the actual force of the explosion, without the hydroplanes jamming.
- The boat may merely be shaken, cut-outs fused, and the electric light consequently extinguished; in such instances, as a rule, she will not come to the surface, but the morale effect is considerable.
- IS OIL SEEN ON THE SURFACE ANY PROOF OF A SUBMARINE HAVING BEEN DESTROYED?
Not unless it is accompanied by air bubbles or continues for a considerable time. German submarines are fitted with an arrangement for ejecting oil fuel and use this to mislead or delay their pursuers.
Oil rising to the surface may sometimes indicate a submarine proceeding submerged or lying on the bottom with her external tanks leaking. A depth charge causes considerable discolouration of the surrounding water, which should not be mistaken for an oil leak.
Oil and bubbles frequently indicate the wreck of a sunken surface ship. The only certain ways of verifying the destruction of a U-boat are by picking up some of the crew, by obtaining some wreckage which had been inside the boat and afterwards floated to the surface or by sending down a diver.
- WHAT TYPES OF TORPEDOES ARE FIRED BY U-BOATS?
They may be driven by compressed air or electricity.
The air-driven type have the longer range and may show a distinct track, particularly in calm or phosphorescent water. If this track shows bubbles on the surface the torpedo will be from 100 to 300 yards ahead of the leading bubbles. Occasionally, when running shallow, their engines may be heard.
The electric torpedoes are cheaper to produce than the above type but their performance is not so good. It is probable that they will gradually replace the air-driven type in U-boats. Their engines have been known to make a faint hum.
The explosive in the head of the torpedo is detonated by a "pistol" which may fire on contact with the target or on reaching her magnetic field. Most (if not all) torpedoes carried by U-boats have combination pistols which will fire by contact or magnetically.
A torpedo with a magnetic pistol may detonate without hitting the target, when making a faulty run or when completing a normal run -- particularly in a rough sea. Any type of torpedo may explode on hitting the bottom.
NOTE. -- The following information has been promulgated:
"Any loud explosion which cannot be identified as being caused by an aircraft bomb or depth charge is probably due to a torpedo. Any ship hearing such an explosion should immediately suspect the presence of a U-boat and take action accordingly."
- WHAT MEANS OF ESCAPE ARE OPEN TO THE CREW OF A DAMAGED U-BOAT?
At a depth of water up to 20 fathoms under good conditions, a number of the crew might be saved by an apparatus similar to the "Davis lung." U-boats also carry collapsible boats in their upper deck casings but these would probably not accommodate the whole crew.
- HOW IS A U-BOAT PROPELLED -- (a) ON THE SURFACE, AND (b) SUBMERGED?
- By her Diesel engines. She might use her motors if she wished to be silent. For instance, at night she might use her electric motors if approaching the enemy's coast in order to send in a boat. She might also use them when stopped on the surface at night in order to turn the boat and bring her sights on the target.
- On her electric motors. These motors are fed from large storage batteries.
When submerged, Diesels cannot be used as they require a continual supply of fresh air to the engines.
VICHY FRENCH SUBMARINESThese submarines are included in order to complete the coverage of continental navies. Not more than a third of the pre-war fleet is believed to be in operating shape. French submarines, though having few classes, vary considerably within the types. Some ships have been reported seized and operated by the Germans. In view of this, radical changes may be expected in the normally oversize French conning towers.
Classes Length Tonnage Armament Tubes MORILLOT 302'6" 1,635/2,100 1-3.9" 8-21" REDOUTABLE 303' 1,384/2,080 1-3.9" 11-21.7" AURORE 241' 893,1,170 1-3.9" 9-21.7" REQUIN 257'7" 947/1,441 1-3.9" 10-21.7" SAPHIR 216'6" 699/925 1-3" 5-21.7"
32 Mine chutes
SIRENE 210' pp
Vichy French Submarine Classes
- HOW DOES A U-BOAT CHARGE UP HER BATTERIES AND HOW LONG DOES IT TAKE?
The U-boat must be on the surface when charging her batteries. The Diesel engine revolves the motor armature which is on the main shaft. The motor then become a dynamo and supplies electricity to the battery.
The U-boat can charge while stopped by unclutching both her propellers, but she would not do so while on patrol as she needs to be under way so as to be able to dive in an emergency.
When a battery is nealry exhausted it takes at least 6 hours to charge it up fully. The necessity for coming to the surface for this purpose is a continual source of anxiety to the U-boat's captain. The periods of long daylight and bright moonlight are very trying, particularly when aircraft and hunnting vessels are likely to arrive and force him to dive.
- HOW DOES A U-BOAT DIVE AND MAINTAIN HER DESIRED DEPTH?
By filling ballast tanks and by the use of hydroplanes, i.e., horizontal rudders.
The larger U-boats have double hulls. The outer hull is of light plating and the space between the two hulls is divided into compartments which form the ballast tanks.
The 250-ton U-boats are single-hulled and the ballast tanks are inside the boat.
When the ballast tanks are filled the U-boat will float awash or sink slowly. While flooding, the boat proceeds ahead on her motors, the hydroplanes are run over to the "dive" position and force her under. By using "rise" or "dive" helm on the hydroplanes the U-boat is maintained at the required depth.
When bringing the boat to the surface compressed air is used to blow the water out of the ballast tanks and give her buoyancy. Fine adjustments of ballast may be made by means of an electric pump.
By using high speed and plenty of "rise" or "dive" helm a submarine may be held on the surface awash when bodily heavy or forced under when bodily light.
- WHAT IS THE BEST PLACE IN WHICH TO HIT A U-BOAT WITH GUNFIRE WHEN SHE IS SIGHTED ON THE SURFACE?
The ideal shot is a direct hit at the base of the conning tower.
With the exception of the conning tower, practically the whole of the hull showing above water is superstructure. This is built of light plating and designed as stowage for ropes, wires, boats, etc., also to give the submarine a streamlined shape when diving. This plating can be shattered by gunfire without endangering the U-boat or preventing her from diving.
When a U-boat has full buoyancy only about 2 feet of pressure hull is above the surface. This presents a very small target and, being rounded, is difficult to penetrate. A hit where the conning tower joins the pressure hull would flood the former and possibly the latter if she is starting to dive.
- WHAT MEANS OF COMMUNICATION ARE USED BY U-BOATS WHEN SUBMERGED?
It is probable that some form of short-distance intercommunication, 10 to 15 miles, can be used by U-boats when diving.
They cannot send wireless messages when totally submerged but they can probably transmit when the periscope only is showing above the water. Wireless messages, however, can be received when diving.
- WHERE SHOULD LOOK-OUTS BE POSTED AND UPON WHAT BEARINGS SHOULD THEY CONCENTRATE?
NOTE. -- The following suggestions do not cancel any orders contained in official publications or received from responsible officers.
When posting look-outs, conditions of visibility, sea, and light should be considered. Three look-outs are essential, one to search ahead, using the crow's nest if the weather is suitable, and one on either side. If sufficient hands are available, a look-out should be posted aft and the side look-outs doubled.
Normally a U-boat on the surface can sight any surface vessel or aircraft -- unless the latter is coming out of the sun -- before she herself is seen. In certain conditions, however, a ship and a U-boat may sight each other simultaneously. Cases have occurred when a U-boat at fairly close range on the surface has been sighted at dawn or dusk, in fog, in the moon's path and when emerging from a clearly defined drifting squall. On such occasions the prompt action of a look-out may enable a ship to fire her gun or ram a U-boat before she can dive. In a "patchy" fog, forecastle and crow's nest look-outs are particularly valuable.
The principal arc to be searched is from right ahead to two points abaft the beam. Any U-boats sighted from right ahead to the bow would probably be at long range so the look-out on that arc should have binoculars if possible. The arcs between 4 and 10 points on either side require the most thorough search as it is there that a periscope or torpedo track is most likely to be sighted. When look-outs are double-banked, one man on each side should use binoculars and the other should search for torpedo tracks and periscopes near the ship. The naked eye has a wider field of vision than binoculars and the latter are perhaps being cleaned when a periscope is showing.
By night, when a U-boat might be creeping up on the surface from astern, look-outs should be posted on either quarter, if possible, with night-glasses.
- WHEN NOT IN CONVOY WHAT ACTION SHOULD BE TAKEN ON SIGHTING A PERISCOPE OR A U-BOAT ON THE SURFACE?
Immediate action should be taken as follows, in this order of priority, when sighting a periscope:
1. Alter course and increase to full speed.
2. Man the guns and Lewis gun.
3. Send the special signal.
4. See that smoke floats are ready for burning.
- If the periscope is at close range and before the beam, steer so as to ram. The U-boat probably will increase speed to 5 to 7 knots and attempt to dive deep. your action will at least have the effect of spoiling her attack.
When sighted at long range, also when on or abaft the beam, turn stern on.
Increase to full speed on all occasions. The main object is to present a small end-on target, instead of a beam shot, by turning through the smallest arc.
- Rouse the gun's crew and pass down the bearing of the periscope. A few shots from a Lewis gun at the last sight position would assist. Point of aim should be ahead of the periscope, a near miss might damage the glass and would "fluster" the attacker. If at close range, fire the Lewis gun.
- Pass the word at once to the wireless operator to send the special signal. If this is received, it may save your own and other ships.
- Prepare your smoke floats. If the U-boat fails with her torpedoes she may surface and attack with her gun. If she can out-range your ship and has a higher speed, the smoke may prove a valuable protection, particularly in a head wind or a light stern breeze.
If a U-boat is sighted on the surface at long range or well abaft the beam turn stern on and proceed at full speed. Do not use your gun or smoke floats unless she starts to chase.
Should you suddenly meet a surfaced U-boat at close range and before the beam, for instance at night or in a fog, turn to ram at full speed, steering well ahead to allow for her advance. Fire with your Lewis gun at her bridge and gun position if within 1,000 yards. If it is obvious that you cannot ram, turn to enable your gun to bear; point of aim being the base of her conning tower.
That the commanding officer of the merchant vessel is not always helpless in the presence of enemy submarines is illustrated by the following narrative of a resolute and daring master:
"SHORTLY AFTER 8 P.M. WHILE STEERING TRUE AND USING ZIGZAG NO._____ (NOT IN CONVOY) WE SIGHTED A PERISCOPE WITHIN ONE HUNDRED YARDS TO PORT ON SIX POINT BEARING. THE WIND WAS THEN NNW, FORCE SEVEN; CLOUDY; SQUALLY; SEA ROUGH WITH A CROSS CONFUSED SWELL, VISIBILITY VARYING DOWN TO TWO AND ONE-HALF MILES.
"EVASIVE ACTION WAS AT ONCE TAKEN, THE SUBMARINE BEING BROUGHT ASTERN. THE PERISCOPE WAS AGAIN SIGHTED IN OUR WAKE AND IT IS MY SUBMISSION THAT THE STATE OF THE SEA AND THE WASH FROM OUR PROPELLERS FORCED HIM TO THE SURFACE CAUSING HIM TO DISPLAY HIS CONNING TOWER.
"FIRE WAS IMMEDIATELY OPENED WITH THE SIX INCH, THREE INCH AND AFTER OERLIKONS. THE OERLIKONS AT ONCE REGISTERED ON HIS CONNING TOWER BUT THE FIRST ROUND OF THE SIX INCH TOOK THE WATER AT THE EXTREME END OF HIS LENGTH AND RICOCHETTED , AS DID THE THREE INCH. THE NEXT ROUND APPEARED TO TAKE HIM ABOUT THIRTY FEET ABAFT HIS TOWER, A BLINDING FLASH BEING SEEN AS THE RESULT OF THE EXPLOSION OF THE SHELL. A THIRD SHELL FROM THE SIX INCH TOOK HIM AT ABOUT TWENTY FEET ABAFT THE CONNING TOWER; HE WAS THEN AT AN INCLINATION OF FROM TEN TO FIFTEEN DEGREES TO THE LEFT. THIS SHELL, FOLLOWED BY ONE FROM THE THREE INCH WHICH BURST AT THE BASE OF HIS TOWER, APPEARED TO ENTER HIS HULL AS A DEEP MUFFLED ROAR FOLLOWED ALMOST IMMEDIATELY AFTER ITS ENTRY INTO THE WATER WHICH COULD NOT HAVE BEEN ANY MORE THAN SIX INCHES OVER HIS HULL. HIS BOW CAME UP TO AN ANGLE OF 35 DEGREES TO THE HORIZONTAL AND HE DISAPPEARED FROM SIGHT, STERN FIRST.
"IT IS OUR CONSIDERED OPINION THAT THE RASCAL WAS DEFINITELY DESTROYED."