(Tuesday, July 31, 1945; during Potsdam Conference of World War II) — The atomic bomb, codenamed “Little Boy,” was successfully assembled today on Tinian Island and is now ready for deployment against Japan.

Video: 'American Experience: Truman' (July 31, 1945, at 2:07:57)

The weapon, which will become the first atomic bomb used in warfare, is set to be dropped on a Japanese target as early as tomorrow, marking a pivotal moment in the ongoing conflict.