USN BD Intelligence Bulletin June 1945 Vol. 2 No. 3
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U.S. NAVY BOMB DISPOSAL Intelligence AUGUST 1945 BULLETIN Vol. 2, No. 3 CONTENTS Japanese Bomb Shackles ..... I Jap Hollow Charge Ordnance 6 Japanese Demolition Equip ment ................................. 14 Delayed Action M ine........... 1 8 Booby-Trapped Ammunition Dumps ............................... 1 9 1 Japanese Sabotage Devices.. 2 0 Linear Shaped Charge Attack on VT F u zes..................... 2 5 Theory of Bomb Disposal At tack ................................... 2 9 Modification of BuOrd Re quests ................................ 3 1 Acknowledgments................. 3 2 Notices ......... Inside Back Cover This document is issued to graduates of a course in Bomb Disposal, by the Officer in Charge, Navy Bomb Disposal School, under authority of Bureau of Ordnance letter F4I — 6 (L) of 22 April 1944. It is for in formation and guidance only and is not a Bureau of Ordnance Publication. It should be destroyed when of no further use to Bomb Disposal Personnel. In view of the fact that Bomb Dis into three general classes, namely: posal personnel may be called upon manually operated, explosive oper to remove bombs from crashed and ated, and electro-magnetic operated. captured Japanese bombers, the fol Japanese Navy planes are equipped lowing general information on bomb with either the manually operated or racks and shackles used by the the explosive operated shackles. Army Japanese Air Corps is given. planes are equipped with any one Japanese Army and Navy bomb of three standard electro-magnetic release shackles in standard use fall operated shackles. Typical.Nagy Bomb Rack Showing Arming Vane Stops CONFIDENTIAL attached to the safety lever. Pulling the safety lever disengages a projec tion on the end of the safety lever from a cutaway portion on the cam- | ming surface of the release lever. When the release lever is pulled, it Manually Operated (Now) Shackle Used frees the shackle hook. The weight on "Val" of the displacement gear and bomb forces the hook open and the displace ment gear swings down and forward releasing the bomb. The picture below also show the arming vane stops used with this type of shackle. One stop is attached to the displacement gear and another Safety Lever Pulled (Side Plate Removed) is attached to the fuselage of the plane. This is the standard and only method used on Navy planes for pre venting the arming vanes from rotat ing while in flight. It should be noted in this connection that it is not possible to jettison safe any Japanese Release Lever Pulled Displacement Gear Finger Released Manually Operated The shackle pictured above is a manually operated fuselage shackle used on the "Val," a Navy dive bomber Type 99 carrier borne Model 11. The "Val" Model 11 is now obsolete but the Model 22 is still in production and possibly uses the same shackle. Also pictured is the displacement gear used on the "Val." The shackle releases the displacement gear which then swings downward and forward due to the weight of the bomb. The bomb is released automatically at the lower limit of movement of the displacement gear. The shackle is operated by pulling a steel lanyard which leads up to the cockpit from the release lever on the shackle. Prior to pulling the release lever the pilot pulls another lanyard "Val" Displacement Gear CONFIDENTIAL Manually Operated Ncny Shackle Used on Nell Release Lever Pulled Trigger Released Navy bomb from a Japanese Navy Explosive Operated bomb rack. Shackles The "Val" is reported to carry one 250 kg. bomb under the fuselage. The explosive operated shackle pic The "Nell" a Navy Type 96 Land tured below is the shackle coming Attack plane, now obsolete, used the into general use on many Japanese manually operated shackle pictured Navy planes. Though designated an above. This shackle has no safety explosive operated shackle, it may lever, but operates by merely pulling also be operated manually. a lanyard. This releases the trigger In general the operation is as fol arm with a caroming action, causing lows. A small electrical cartridge is three notches or cogs in a half moon inserted below a steel plunger in the gear to engage cogs in a like portion body of the shackle. When the car on the opposite hook. This motion tridge is fired by closing the electric opens the suspension hooks releasing circuit, the plunger device is driven the bomb. forward by the force of the explosion. ) The "Nell" is reported to have In the shackle pictured below the carried a 800 kg. or a 500 kg. or two plunger turns the locking lever free 250 kg. or twelve 30 kg. bombs. It ing the suspension hooks. The hooks also was reported to carry an 800 kg. turn due to the pull exerted by a torpedo. However, according to avail connecting rod running from the able information only the 60 kg. bomb locking lever to one of the hooks. is carried on the shackle pictured. The opposite hook is forced to move Explosive Operated Navy Shackle Used Piston Releases Trigger on Betty’ Explosion Pushes Piston Hooks Open CONFIDENTIAL 3 as it is geared to the driven hook. This forces the hooks open and re leases the bomb. The shackle pictured is used on the "Betty." The "Francis" uses an ex plosive operated shackle, for large bombs, which operates very much the same but the explosive operated hook merely frees the displacement gear from the fuselage. Actual release of the bomb is accomplished by a system of levers which automatically open the hooks as the displacement gear swings downward. When the displacement gear and bomb have moved down to a point approximately 40° with respect to the axis of the plane, the locking lever is released and the bomb suspension hooks are opened allowing the bomb to fall. A wiring diagram of the Type 0 six-bomb release panel found on the "Francis" indicates that the bombs carried may be dropped in salvo or independently with a time interval of release of the forward and rear bombs from 0.25 to 6 seconds. Three Types o f Electro-Magnelically Op The "Francis" also has a small erated Shackles Used on Army Bomb bomb release mechanism in the for Racks ward part of the fuselage for carrying 30 and 60 kg. bombs. This rack is known as the Type 97, small bomb Electrically Operated release mechanism. Sh ackles Operation of the shackle is basically Three standard Army fuselage the same as the explosive operated shackles with electro-magnetic re shackle found on the "Betty." Two lease have been recovered to date. battery leads from the cockpit enter A new series of shackles are expected the rear of the bomb rack and lead out on new Army planes. to an electrical cartridge on the shackle. When the electrical car Japanese Army bomb racks, con tridge is fired, the operating plunger is trary to the system found in Navy driven up against a rocker arm. The racks, use arming wires instead of rocker arm releases one of the hooks arming vane stops. Thus it is possible and also strikes a cam block, which by to jettison safe Army bombs when its cammed surface forces the opposite dropped from Army planes. hook to open releasing the bomb. The release unit is a simple electro- The "Francis" is reported to carry magnetically operated double trip- one 800 kg. bomb or two 500 kg. trigger mechansim and should nor bombs. In addition it carries two 60 mally present no difficulty to B. D .(’ kg. bombs forward of the bomb bay. personnel required to recover bombs 4 CONFIDENTIAL Hooks Open from the bomb racks of a crashed aircraft. Army Electro-Magnetically Operated The suspension hook carrying the Shackle bomb is locked in the closed position by a safety catch. When current passes into the shackle a magnetic field is established which pulls the safety catch away from the trigger release allowing it to move up. This motion releases the hook lock and allows the hook to swing down releasing the bomb. Pictured above are the three types of electrically operated shackles. The various stages in operation of one of the shackles Safety Catch Released is shown and should be self-ex planatory. It is not possible to say just which Japanese planes will have a certain type of bomb rack as sufficient in formation is not available at present. It is hoped, however, that the above will give a general picture of what can be expected in the various types of shackles. In addition to the above discussed fuselage racks and shackles, are various types of wing racks which have been recovered, but as their operation is almost identical to fuselage racks of the same type, no detailed discussion is necessary. Navy wing racks like Navy fuselage racks are either manually or explosive operated, and Army wing racks as far as is known are electro-magnetic operated. Wing racks are in general small and designed to carry small bombs on Hook Lock Released fighters and light bombers. CONFIDENTIAL 5 3. Bombs: nitroanisol, 40% RDX) Explosive." (a) kg. hollow charge bomb. Small model—"Bursting charge for (b) 1 kg. hollow charge bomb. temporary designated hand thrown 4. Torpedoes: conical grenade." The explosive used (a) Mentioned in documents only. in the small model was found by analysis to be pentolite but as this was 5. Demolition charges. designated an experimental round it These items will be .discussed in is possible that future recoveries may the order listed and will be supple contain Type 94 explosive as this is mented by information from docu designated in documents as the stand mentary sources where such informa ard explosive for use in hollow charge tion is thought to be correct.