The Ke-Go

As the war progressed the Japanese came to see the invasion of the home islands as a very real threat and various means of attacking the invasion fleet were investigated. One possi­bility was a bomb capable of homing in on the heat emissions of naval vessels. The plan called for the bombs to be used in night attacks when heat signatures of the ships would not be masked by the sun and other ambient heat sources. The project was undertaken by the IJA and given the name Ke – Go and work commenced in March 1944. The First Military Arsenal’s Omiya Department in Tokyo undertook development of the bolometer that would detect heat in the infrared wavelength and bench testing showed that the mechanism was workable. In fact, the sensor could detect the heat from a man’s face at 100m (328ft)! For the bomb to carry the bolometer, three different types were investigated: the B-l, B-2 and B-3. Of the three, only the first showed potential and the remainder were abandoned. A myriad of men and departments were assigned to the task of realising the B-l. Under the Military Ordnance Administration Board was Major Fujita who oversaw the gyro and airframe, Major Hizuta who also worked on the air­frame research, and Major Sonobe who addressed the amplifier. The Seventh Military Laboratory encompassed Professor Konishi of the Shikan Gakko in Osaka who handled the mathematical work, Professor Sano of the Osaka Imperial University who conducted the electrical design and Dr. Itakawa of the Aeronautics Research Laboratory who undertook the aerodynamic design studies. All wind tunnel testing was held at Rikugun Kokugijutsu Kenkyujo.

The first two bomb versions, the Ke-Go 101 and 102, were built in small numbers: ten and five respectively. The hydraulic and mechan­ical linkages for operating the bomb ailerons, coupled with the use of an electric gyro that interfered with the bolometer (A bolometer is a device used to measure the energy of inci­dent electromagnetic radiation and was invented by Samuel Pierpont Langley in 1878.), saw both of these versions aban­doned. Continued study resulted in the Ke – Go 103, 104 and 105. However, none of these designs left the drawing board although the 103 was to use an air gyro instead of an elec­trical version. The gyro only existed to ensure the bomb did not spin faster than 360° in 50 seconds. The Ke-Go 106 would be the first to be built in numbers, fifty examples in all. Overall length of the 106 was 4.7m (15.5ft) long and the wing span was 2m (6.5ft). Four main fins were fitted 1.7m (5.7ft) down the length of the bomb body with a smaller set of four fins 1,2m (3.9ft) behind the main fins, and the tail of the Ke-Go contained dive brakes. In the nose was the bolometer while the shape charged warhead was contained behind it. Two strikers that protruded out from the nose were tipped with small pro­pellers which spun and armed the bomb after release. The strikers served as the impact fuse, but a delayed fuse was also installed should the bomb strike water, in which case it would explode beneath the waterline of a ship. In short order, the Ke-Go 107 joined the program with a total of 30 bombs. The 107 had similar dimensions to the 106 version and weighed 726kg (1,6001b).

The Ke-Go was guided in flight by the bolometer. The bolometer was part of a unit that consisted of the bolometer itself, a mir­ror, motor, distributor, amplifier, relay box and battery. Heat sources passing through the bolometer would strike the mirror that, depending on where it struck, would trigger the amplifier which operated the ailerons, steering the bomb towards the heat source. The use of dive brakes slowed the plummet of the bomb, allowing time for the bomb to make adjustments in flight before impact. The ailerons could move up or down 20°. For a warhead, the Ke-Go carried between 200 to 300kg (440 to 661 lb) of shaped charge explo­sive, depending on the model. Perhaps in error, a 1946 US Navy report lists the warhead as ranging from 20 to 30kg (44 to 661b) of explosive which is very light for the size of the Ke-Go.

With enough bombs ready and available, field testing began without the bombs con­taining any payload. The test used a floating raft which measured 10m (32.8ft) by 20m (65.6ft) and was anchored in Lake Hamanako (located in Shizuoka Prefecture). On the raft wood and coal in a 4m (13ft) by 4m (13ft) pile was set alight. Both Ke-Go 106 and 107 bombs were released from altitudes varying between 1,524m (5,000ft) and 3,048m (10,000ft) but the results proved very disap­pointing. In all, around 60 drops were made but only 5-6 of the bombs displayed the zig­zag flight path that indicated the bolometer was sensing the heat from the fire and guid­ing the bomb. The remainded simply veered away from the raft. The dismal results were blamed on faulty equipment although the data collected was not sufficient to properly identify the cause of the failures. It was found that the terminal velocity of the Ke-Go 107 was 539km/h (335mph). In July 1945, further testing ceased, though work continued on improving the bomb.

The Ke-Go 108 was developed but it was with the Ke-Go 109, the last to be designed, in which the Japanese hoped the problems would be resolved and the bomb would finally prove successful. The Ke-Go 109 bomb was 5.5m (18ft long), 5m (1.6ft) in diameter, had a wingspan of 2.9m (9.4ft) and weighed 800kg (1,7641b). It was estimated that the ter­minal velocity for the Ke-Go 109 was 579km/h (360mph). It featured a larger wing span because the smaller span was considered to be one of the main causes of the poor perfor­mance of the Ke-Go 106 and 107. It was antic­ipated that the 108 and 109 bombs would be ready for test drops by September 1945. Of course, the end of the war ensured this would never happen and neither bomb was built.

Had the Ke-Go made it into service, the car­rier was to be the Ki-67 Hiryu (codenamed Peggy by the Allies). The bomb required a special brace that was fitted into the bomb bay, the apex of the brace extending a few inches past the exterior of the doors. The bomb was secured to this and the lower wing could fold to give ground clearance. On take­off, a crewman had to lower the wing and did so by means of a crank that activated a servo in the bomb, which then moved the wing. The bombardier would use bombing tables appropriate for the weight of the weapon and on release the bomb’s arming wires were pulled out along with a wire that released the dive brakes. Typically, the bomb would be dropped from 2,000m (6,562ft). After the bomb was away, the Ki-67 saw a 64km/h (40mph) increase in speed.

All of the bombs were built from wood. The only metal components consisted of the nose cap containing the bolometer and the dive brakes. In all cases, the bomb bodies were built by the Atsu Department of the Nagoya Arsenal, the gyroscope by Hitachi Co., the spring/gear parts for the timing mechanism by the Hattori Jewellery Co. and the electrical contacts for the timing mechanism by Sumit­omo Communications Branch.

Interestingly, the US would develop a simi­lar weapon, the VB-6 Felix. This was a 454kg (1,000 lb) bomb fitted with an infrared seeker in the nose that controlled the fins and guided the bomb. It was meant for night warfare, notably against ships at sea. The VB-6 was put into production in 1945 but would not see ser­vice by the close of hostilities.

Both the IJA and the UN developed spe­cialised bomb munitions during the war, some of which remained projects while oth­ers saw service. Several were dedicated to the practice of air-to-air bombing in which bombs were used to attack enemy bomber forma­tions. Although not a complete list, the follow­ing are some of the more interesting examples.

Ko-Dan

The Japanese expended some effort in devel­oping the Ко bomb. This was developed in response to observations made by one Kobayashi of high-speed photographs of det­onations of various experimental shaped charges. The basis of his theory was that the energy produced by an explosion is projected along horizontal lines with the impact sur­face. By extension, the amount of energy cre­ated is proportional to the quantity of the explosive used. To achieve a wider impact area against a target, the Ко bomb had a 2mm thick rubber nose that was mated to a 2mm thick steel case. On impact the nose of the bomb would flatten and expand, thereby enlarging the surface area and increasing the effects of the explosive pellets contained within. The Ко would be used against hard targets such as concrete emplacements. In tests, a Ко bomb with 50kg (1101b) of TNT and ultropine in an even split mixture could penetrate a lm (3.2ft) slab of concrete and utterly destroy it. It would take a regular 250kg (551 lb) bomb to accomplish the same effect. A part of this concept is known as the Misz- nay-Schardin Effect and is in practice today with modern HESH (High Explosive Squash Head) munitions and EFP (Explosively Formed Penetrator) weapons.

Mk. 7 (IJN)

Conceived around 1936 by Dai-Ichi Kaigun Koku Gijutsu-sho, the Mk. 7 chemical bomb was not given priority since at the time there was little need for such a weapon and it was thought the work needed to bring it to fruition would be too great. The idea surfaced near the end of the war, the Mk. 7 then being denied a second time in favour of guided missiles. The design was based on the 1kg (2.21b) prac­tice bomb. It had a rubber nose and within a special tail was a glass bottle of Bacillus bac­teria, most likely B. anthracis, which causes anthrax. It had no fuse or explosive charge, the impact being enough to break the bottle and release the bacteria. The planned colour for the bomb was a purple nose with a purple tail.

Mk.19 (IJN)

This was an air-to-air rocket-propelled bomb design intended for use against bomber for­mations. It weighed 7.5kg (16.5 lb). Although it was never built, the work eventually resulted in the Mk. 28 rocket bomb.

‘Silver Paper Scattering Bomb’ (IJN)

This was the Japanese version of the German Diippel, better known as ‘Window’. A 2kg (4.41b) sheet steel cylinder was packed with 200 pieces of metal coated paper measuring.3m x 8.4m (1 ft x 27.5ft). The bomb used a pull fuse that the crewman yanked to arm it and was then thrown out of the aircraft, the sub­sequent charge expelling the papers into the air to act as false radar targets. This anti-radar weapon was used heavily from 1944-1945.