The recent 7:10 to Tokyo article, Unexploded WWII Bombs In Japan- How Many Are Out There?, provoked some interesting responses but it came as a bit of a surprise to hear from someone who was actually on the ground in Japan disposing of these remnants from WWII. Roy Kaiser took an interest this article and provided a lot of food for thought in his well-researched comments. Roy had a fifteen-year career in Explosive Ordnance Disposal (EOD) for the US Army and spent three of those years (1967-1970) at Ikego Army Ammunition Depot in Kanagawa Prefecture. He has generously agreed to share some insights on how bombs work, how they are disposed of and has provided some interesting newspaper clippings from the time. Roy retired in 1976, after 24 years of service. He often recalls the time he served with the 97th and fondly remembers the great guys he served with.

The 97th Explosive Ordnance Disposal (EOD) was the last US Army Explosive Ordnance unit stationed in Japan (deactivated in 1970) and was based in Zushi City, about 40 kilometers (25 miles) outside of Tokyo. Roy was assigned to this unit from 1967 - 1970 and recalls participating in the disposal of three unexploded bombs (UXB) during that period. In his comments on Unexploded WWII Bombs In Japan- How Many Are Out There?, he states that between November 1, 1944 and August 15, 1945 American B29 Superfortresses dropped more than 11,000 bombs, weighing 500 pounds or more, on Tokyo alone, destroying 51% of what is now the worlds largest city. Historically 5-20% of military high explosive munitions fail to function as intended (duds). Given those failure rates somewhere between 500 and 2,200 unexploded bombs would have been left behind after WWII.

So why didn’t theses bombs detonate? Roy explains that the general purpose, high explosive, bombs that were dropped on Japan had three main types of fuses resulting in detonation on impact (nose and tail impact inertia fuse), detonation after surface penetration (tail impact inertia fuse), or delayed action detonation up to 144 hours after impact (tail fuse).

When a bomb is dropped an arming wire is normally withdrawn from the arming vane, which looks like a little windmill, and the vane then rotates a rod that arms the fuse which causes the bomb to detonate. If the bomb came out of the plane without the arming wires being extracted the bomb would impact the ground without detonating and would leave a penetration hole rather than an explosion crater. Another possibility is that the bomb’s firing pin could fail to strike the detonator or get hung up by some type of obstruction, in which case the bomb could detonate with the least disturbance. To further complicate matters, most bombs had an anti-withdrawal feature that prevents the adapter booster and fuse from being unscrewed from the bomb by a locking pin. If an attempt was made remove this portion of the bomb, the licking pin would activate the fuse and the bomb would detonate. (Bomb diagram)

Tokyo’s Real Boom Town article circa 1967

After a bombing raid, Japanese civil defense officials would scour the area bombed to look for impact craters. US UXB reconnaissance procedures would include probing the penetration hole with a long non-magnetic rod to determine the trajectory of the bomb and its final resting place. The location of the bombs would then be recorded on a map similar to the one that you see below.

Map of UXB locations in what appears to be Yurakucho, 1 Chome

Once the unexploded ordnance is located, a variety of different disposal methods are available to the EOD teams. The decision is often a difficult one as there is a need to balance risk to the EOD team with magnitude of the damage that would result if the unexploded bomb were to detonate. The options include remote on-site detonation, removal and transport to a remote destination for disarming and/or detonation, or a hands-on disarming of the ordnance on-site. The latter method carries the most risk for the EOD team and is only utilized to protect lives, very important property, materials, or facilities. The safest way to dispose of UXB is to evacuate the area, take measures to protect against blast damage, and then detonate the bomb in place. This option is usually not available in densely populated areas like Tokyo.

(Images courtesy of Roy Kaiser)

Part 2 of this article can be found here

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