Plans for the invasion of Japan incorporated an Alsos Mission . Japanese fire balloon attacks on the United States had aroused fears that the technique might be used in combination with biological agents , which the Japanese Unit 731 was known to be experimenting with . In March 1945 , the physicist and seismologist L. Don Leet was appointed as head of the scientific section of the Alsos Mission to Japan . Leet had previously worked with the Manhattan Project on the Trinity nuclear test . Plans were drawn up to prepare and equip a T-Force along the lines of the one in Europe , but made up of personnel already in the Pacific . The mission differed from its European counterpart in that it was solely American and consisted of only one intelligence agency . Responsibility for nuclear matters was subsequently handled by a separate Manhattan Project Intelligence Group organized by Groves
Trinity nuclear test
Trinity (nuclear test)
Alsos Mission