Charles Sweeney
Poor bombing visibility and an increasingly critical fuel shortage eventually forced "Bockscar" to divert from Kokura and attack the secondary target, Nagasaki. As they approached Nagasaki, the heart of the city's downtown was covered by dense cloud, and Sweeney and the plane's weaponeer, Commander Ashworth, initially decided to bomb Nagasaki using radar. However, a small opening in the clouds allowed "Bockscar's" bombardier to verify the target as Nagasaki. As the crew had been ordered to drop the bomb visually if possible, Sweeney decided to proceed with a visual bomb run. "Bockscar" then dropped "Fat Man", with a blast yield equivalent to 21 kilotons of TNT. It exploded 43 seconds later at above the ground, at least northwest of the planned aim point. The failure to drop "Fat Man" at the precise bomb aim point caused the atomic blast to be confined to the Urakami Valley. As a consequence, a major portion of the city was protected by the intervening hills, and only 60% of Nagasaki was destroyed. The bombing also severed the Mitsubishi arms production extensively and killed an estimated 35,000-40,000 people outright, including 23,200-28,200 Japanese industrial workers, 2,000 Korean slave laborers, and 150 Japanese soldiers.
RDS-1
The RDS-1 explosion yielded 22 kilotons of TNT, similar to the American Gadget and Fat Man bombs. At Lavrentiy Beria's insistence, the RDS-1 bomb was designed as an implosion weapon similar to the Fat Man bomb dropped on Nagasaki, Japan; RDS-1 also had a solid plutonium core. The bomb designers had developed a more sophisticated design (tested later as RDS-2), but rejected it due to the known reliability of the Fat Man type design, the USSR having received extensive intelligence on the design of the Fat Man bomb during World War II.