Walter Goodman joined the Special Engineer Detachment at Los Alamos in 1943. Goodman worked as an electrical engineer on the implosion bomb with Manhattan Project scientists Luis Alvarez and Harold Agnew. He witnessed both the Trinity test and the atomic bombing of Nagasaki.
In July 1945, Goodman travelled to Tinian to help prepare the Fat Man bomb to be dropped on Japan, as part of Project Alberta. On August 9, 1945, Goodman joined Lawrence H. Johnston and William L. Laurence, a correspondent for the New York Times, on board the instrumentation aircraft, The Great Artiste, as part of the Nagsaki mission. Goodman, who had a video camera with him, took motion pictures of the mushroom cloud above Nagasaki.