Fire Balloon - Allied Investigation

Allied Investigation

Despite their low success, the authorities were worried about the balloons. There was the chance that they might get lucky. Much worse, the Americans had some knowledge that the Japanese had been working on biological weapons, most specifically at the infamous Unit 731 site at Pingfan in Manchuria, and a balloon carrying biowarfare agents could be a real threat.

Nobody believed the balloons could have come directly from Japan. It was thought that the balloons must be coming from North American beaches, launched by landing parties from submarines. Wilder theories speculated that they could have been launched from German prisoner of war camps in the U.S., or even from Japanese-American internment centers.

Some of the sandbags dropped by the fusen bakudan were taken to the Military Geology Unit of the United States Geological Survey for investigation. Working with Colonel Sidman Poole of U.S. Army Intelligence, the researchers of the Military Geological Unit began microscopic and chemical examination of the sand from the sandbags to determine types and distribution of diatoms and other microscopic sea creatures, and its mineral composition. The sand could not be coming from American beaches, nor from the mid-Pacific. It had to be coming from Japan. The geologists ultimately determined the precise beaches in Japan the sand had been taken from. By this time, it was mostly irrelevant, since by early spring the balloon offensive was almost over.