The next group of investigators to visit Nagasaki from the U.S. was a party of the Naval Medical Technology Investigation Group called the “Navtac Jap Team.” That team, based at Ōmura, was engaged in investigations in Nagasaki for three months from late September to late November.

   The U.S. military's investigation of the effects of the atomic bombing was conducted from mid-September to late November, almost in parallel with the Japanese side's investigation. As with the Special Committee for the Investigation of Atomic Bomb Damage established by the Japanese side, several groups of experts were dispatched to conduct detailed investigations in various fields. U.S. military doctors examined the bodies of atomic bomb survivors in their hospital rooms, who had been exposed to the Nagasaki atomic bomb and contracted A-bomb diseases and became patients who were rescued and admitted to hospitals.

　The Special Manhattan Engineer District Investigation Group of the U.S. Army was the first to arrive in Nagasaki. Headed by Brigadier General Thomas Farrell, the group consisted of about 30 scientists, including medical and technical teams, who were in Nagasaki from mid-September to early October 1945 to gather information. The first team's main task was to conduct a preliminary study on the effects of the atomic bomb. They measured the level of residual radioactivity for the safety of the American troops occupying Nagasaki.

　The next group of investigators from the U.S. Army to visit Nagasaki was the Naval Medical Technical Survey Group, known as the "Navtac Jap Team" (Navtac Jap Team). Based at the Omura Naval Hospital, the team spent three months, from late September to late November, investigating the Nagasaki atomic bombing. Led by military physician Colonel Stafford L. Warren, the survey team investigated the physiological effects of the atomic bomb. One group belonging to the survey team worked exclusively on measuring radioactivity in Nagasaki. Another Army medical team arrived in Nagasaki on September 30 to investigate the medical effects of the atomic bomb. Colonel Ashley Augustson was the head of planning for the Army Medical Group. The British Army also sent an atomic bomb survey team in November 1945. They investigated the effects of the atomic bombs on Hiroshima and Nagasaki and published their report in 1946.

　On the Japanese side, the Special Committee for the Investigation of Atomic Bomb Damages, established by the Japanese Ministry of Education on September 14, 1945 and first convened on October 24, 1945, conducted an investigation of the effects of the atomic bombs on Japan. The actual work began at the end of September and continued through October. The actual work began in various fields at the end of September and October, and continued for three years until March 1948. However, most of the essential studies appear to have been completed by March 1946. Studies of the hypocenter, heat radiation, and residual radiation levels from the atomic bombs were also completed during this period. The research results of the impact study were published by the Japan Society for the Promotion of Science in August 1951 as a "Summary Report" and by the Science Council of Japan in May 1953 as a two-volume report (1,642 pages) entitled "Atomic Bomb Injury Study Report. The Occupation Forces, GHQ, notified the Special Research Committee on Atomic Bomb Casualty Surveys on December 11, 1945, and placed various censorship and restrictions on the research and publication of the results of the atomic bombing.