Page 76 - Marutas of Unit 731

“Old Type Uji Bomb—By 1938, the trend in Japanese munition development

was towards bombs of simpler design, greater capacity, and requiring a

minimum of explosive for fragmentation and dispersion of the viable

bacterial contents. is objective was not speci cally expressed by Ishii but it

is concluded from his criticism of the earlier munitions and from a

consideration of succeeding bomb development. From steel case structive
effect on the payload, later effort was devoted to design and development of

ceramic and glass case bombs using primacord or primacord and a

minimum of TNT as the explosive charge. e porcelain case Uji bomb was

the result of this trend in bomb development. e original model,

designated by Ishii as the “Old Type Uji” bomb, weighed 25 kilograms and
had a capacity of approximately 10 liters. e exter ior of the porcelain case

contained longitudinal grooves to accommodate the explosive of 4 meters of

primacord. e bomb was lled through an opening in the nose stopped by

a metal screw cap. A celluloid n assembly was strapped to the base of the

bomb. Equipped with a time fuse in the tail, the bomb was designed to
explode in the air at a set altitude with fragmentation of the porcelain case

and dispersion of the contents. e porcelain fragments had little

penetrating force, but were difficult to detect on the ground. e bomb was

tested in 1938 on a eld layout such as for the I, Ro, and Ha bombs using dye

or starch solutions and suspensions of nonpathogenic organisms. In static
tests, exploded at a height of 15 meters, an area of dispersion 20-30 by 500-

600 meters resulted with a wind velocity of 5 meters per second. In drop

tests, areas of dispersion 20-30 by 500-700 meters resulted when the bomb

was exploded at altitudes of 200 to 300 meters. Particle size of the

disseminated liquid contents ranged from ‘droplets the size of raindrops,
and larger drops due to aggregation, to particles 50 microns in diameter.’”