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CHARACTERISTICS OF GERMAN SUBMARINES
Torpedoes may be fired from a depth of 200 feet.
(This is a reasoned conclusion of submarine observers.)
It has heretofore not been necessary to fire from deep submergence.
Italian torpedoes have similar characteristics.
A total of 10 T-type or 15 S-type mines could be carried in the tubes.
Guns can be fired in a moderate sea. To date they have only been used against merchantmen inside of about 3,000 yards.
It is believed they have the best grade binoculars mounted on some kind of an azimuth circle and used as a simple torpedo director. This arrangement is considered to be simple and excellent for night surface firing.
Their periscopes are especially fine. The periscope used for attack is very thin, 1¼ inch in diameter and can be expected to leave little or no wake at slow speed. The periscope used for searching is thicker, 4 inches in diameter. There is reason to believe an altiscope has been incorporated in the design of their periscope for use in searching overhead.
U-BOAT AT PERISCOPE DEPTH
500 Ton -
Thin Periscope -
28½ feet to top of hull.
44 feet to bottom of hull.
Thick Periscope -
20 feet to top of hull.
35½ feet to bottom of hull.
750 Ton submarine may be a few feet deeper.
See C.B. 4002(N) series for latest information. This publication is corrected periodically as new information is obtained.
RADIO DIRECTION FINDERS
Probably can cover low and intermediate frequency bands.
ABILITY TO TAKE BEARINGS OF OUR ULTRA HIGH FREQUENCY TRARSMISSIONS (TBS)
There is no indication that they can take bearings of our ultra high frequency transmissions. It must be assummed they can hear such transmissions.
Sighting records of British Air Force indicate that German submarines are not yet equipped with radar. There are, however, indications that radar mounted on planes can be detected by U-boats.
German Underwater Sound Apparatus
SUBMERGED CRUISING RADIUS
Full Speed (7.44 kts.)
2 hours endurance
Economical Speed (1 shaft)(1.08 kts.)
70 hours endurance
RATE OF RISE
1½ feet per second
½ foot per second
Some German submarines are believed to be equipped with an apparatus for ejecting tablets of chemical substance with slight negative buoyancy, which while sinking slowly, create for a period of about six minutes a bubble screen comparable in size to a submarine target. The submarine may attempt to keep this screen between herself and the anti-submarine vessel. Any ship encountering at close range an echo with a change in pitch at the same time as a clear echo should be alert to change targets.
SURFACE SPEED vs RPM
The data shown herein is from British sources and is issued to British submarines with the following warnings:
1. "Approxipate for general guidance."
2. "Too ruch reliance should not be placed on these figures."
PROCEDURE FOR SALVAGING 4 500-TON U-BOAT
Salvaging an enemy submarine is quite possible if certain steps are taken quickly to prevent scuttling. Even though the possibility may present itself very rarely a few driils can make the difference between a valuable capture and the "one who got away."
All A/S vessels will insure that their organization provides for a salvage party with duties and equipment patterned on the requirements, herein given. This party must be especially trained but may well be organized as part of the repair party.
All hands in the boarding party are to be equipped with .45 automatic pistols, flashlights, and gas masks. One man should carry a tommy gun. A kit consisting of two large and two small Stillson wrenches, hand and tear gas grenades, 30 feet of chain attached to a tool box, a small T-wrench, and a sledge and crowbar should be ready for assembly at all times.
The boarding party should consist of the following men with the following duties:
(a) GUNNER'S MATE to handle hand grenades, tear gas, or Very pistol if there is evidence of resistance. The Very pistol may used to create an intense light inside the submarine to temporarily blind any men left inside.
(b) BOATSWAIN'S MATE to lash one end of chain to deck, dropping end with tool box attached down the hatch. The chain fouls the hatch, preventing any remaining Nazis from slamming hatch shut and trapping party.
(c) TORPEDOMAN'S MATE serves as armed guard, and goes down conning tower hatch first. He is prepared for all types of strong arm methods. After cleaning out main control room and wardroom he goes forward to torpedo room, looking for planted charges and secures torpedoes.
(d) BOARDING OFFICER goes forward to the wardroom and opens the confidential publication safes. One is located in the port bulk head above the captain's bunk. The other is below the small built-in desk on the port side of forward bulkhead. These safes are built-in to the bulkheads and have a key and a combination lock each. Getting the publications is as important as saving the submarine itself. Haste is necessary inasmuch as the time the submarine will remain afloat may be limited.
(e) MACHINIST ONE closes No. 5 main vent valve, the largest wheel valve on forward bulkhead of control room. This valve can be told by its chain drive connections. All vent valves are clockwise to close. After No. 5 is secured he goes to the main air control panel which is the center of three valve panels on the starboard side of the control room abreast the conning tower hatch. He closes the lower left valve of this panel which is the panel drain valve and opens the top two valves and the large master valve at the top center of the panel. After opening master valve and center panel turn to the left hand panel which controls blowing of tanks. Open the top two valves of this panel. Set pressure into these tanks at once by opening master valve at top center of this left hand panel. It is necessary for the men topside to keep alert to notice excessive bubbles, and notify Machinist One immediately of their existence to prevent damage to the ballast tanks. After all tanks have been blown, go to the hydroplane controls on the starboard side of the control room forward, throw them counterclockwise to "hand rise" and secure in position. Hydroplanes set in this position are a great aid in towing.
(f) MACHINIST TWO closes main vent valve No. 1, on the after bulkhead of control room. This also is a chain drive valve, the largest on the bulkhead. He then closes vent valves 2, 3, and 4. These valves are levers, located on the overhead in the after part of the control room. To close them push them up and secure them. As an aid to memory, remember "shut up." Valves 2 and 4 are vents to fuel tanks, and will be closed if there is fuel in tanks. Check to make sure. After closing all vent valves Machinist Two Informs Machinist One so that the latter can blow tanks. Machinist Two then closes all valves grouped around the bilge pump in the starboard after corner of the control room. Do not attempt to operate pump because in the group of bilge valves is located a sea valve; and anyone unfamiliar with German stands an excellent chance of flooding something.
(g) ELECTRICIAN'S MATE goes to emergency light control on starboard bulkhead, in after corner of control room; turning the large wheel there makes and breaks the emergency lighting circuit. If there is no response, go to cabinet on port side of wardroom just aft of the captain's bunk. Turn wheel to select various combinations. If there is any juice left in batteries the lights will work. (NOTE - The wardroom is the compartment just forward of the control room. The captain's bunk is on the port side.)
(h) RADIOMAN goes forward to radio and sound gear on starboard side of wardroom. He aids boarding officer in obtaining publications.
(i) SIGNALMAN stays topside to keep in contact with ship.
Other aids to obtaining buoyancy are:
(a) Dump fuel in No. 2 and 4 by opening valves located on each side forward about 4 feet off deck and also are farthest cornerwise valves aft. These valves are in the control room and are spindles, operated by ratchets.
(b) Do not close Kingston valves during salvage operations. These valves are visible as face plates flush with deck with T-wrench fittings. Smaller valves close counterclockwise and are geared to serve as boosters to larger valves.
(c) If all vents are closed and some buoyancy is needed, order all hands topside and close hatch covers. The hull itself serves as a tank.
Further particulars to be considered are:
(a) Be careful that ersatz material in valves does not break apart.
(b) All valves, except geared boosters in 3205(b), close clockwise to the right.
(c) Emergency lighting will function even if fuses have been removed.
(d) Destruction charges are believed to be used. Most likely locations for charges would be in torpedo rooms forward, wardroom, control room, and motor room aft. As an aid in the "hunt" for hidden charges bring a few of the sub's crew down to help. They will squeal.
German 740-ton U-boat on surface at the instant of sounding crash dive alarm. Pilots will seldom, except by good luck and accident, get close enough to view this scene.
Appearance approximately 18 seconds after starting crash dive. External appearance has not changed materially from Figure I.
Approximately 23 seconds after starting crash dive. Note change since Figure 2 only about 5 seconds before. Time until now has been consumed in flooding tanks, setting diving rudders, and otherwise starting the dive. Submergence is now rapid. Dim outline of submerged portion is shown in this and succeeding figures. This will rarely be seen in the North Atlantic but is shown to retain perspective and proportion. In clear water appearance is similar to that shown here.
About 25 seconds have passed since crash dive was started. Forward part of the boat and most of conning tower are now submerged.
At about 30 seconds bridge rail goes under, forming the distinctive swirl shown here. Only short portion of periscope may be visible above surface.
Submergence complete at 43 seconds. Distinctive appearance of swirl is approximate as shown. Disturbance caused by propellers is visible, but as shown, is not as clearly defined nor as persistent as the swirl.
This figure shows to scale the approximate location of air bubbles relative to a U-boat proceeding at 75 foot depth on a straight course. The U-boat is approximately 240 feet long. The futility of bombing in the vicinity of the bubbles is apparent. Submarine proceeding at 8 knots and under arrow in side view.
This figure, to scale, represents a U-boat at 75 foot depth on a straight course leaving both air bubbles and oil released at the same time. This submarine is proceeding at full submerged speed, and is under arrow in side view.
CHARACTERISTICS OF JAPANESE SUBMARINES
Japanese submarines are divided into three (3) classes. In the first and largest class are the so-called "I" or fleet submarines, all of which have over a 1,000-ton displacement and which in general are constructed along similar lines to the late German U-boats of the first World War. Quite a few of this type are so constructed that they can carry either a midget submarine or an observation type aircraft. The second type consisting of the so-called "RO" or coastal type, are smaller submarines of less than 1,000 tons displacement of an earlier construction, slower speed and less cruising radius. These vessels, however, can easily operate in Hawaiian waters from their bases in the Mandate Islands, and have been contacted in the Aleutian Island Area, and in the Indian Ocean as far to the westward as Madagascar. The third type consisting of midget submarine is of two sub-types, the first of which is represented by those captured at Pearl Harbor, and the second by those captured at Sydney, Australia.
The general outline of all submarines is very much the same. Details of silhouettes, dimensions, armament and engines are shown in ONI 14. The remarks pertaining to the German U-boats apply fairly closely to the Japanese submarines as well.
GENERAL ORGANIZATION OF JAPANESE SUBMARINE COMMAND
At the time of writing the bulk of Japanese submarines are grouped under a single submarine command, the Sixth Fleet, the Headquarters of which is believed to be situated in the Marshall Islands. Besides this, there are about two squadrons each assigned to duty in the Fleet which defends the area which includes the Aleutian Islands, and in the Fleet assigned to the area which includes the Solomon Islands.
Except for dispositions taken soon after the beginning of the war, most of the Japanese Submarine effort has been in reconnaissance and very little toward the destruction of merchantmen.