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.
William Penney, Baron Penney
Along with RAF Group Captain Leonard Cheshire, he accompanied the American Team to Tinian Island from which the Hiroshima and Nagasaki missions were flown. On 9 August 1945 he witnessed the bombing of Nagasaki. The US authorities had controversially stopped them seeing the Hiroshima detonation, but at the last minute Penney and Cheshire were granted permission to fly in the B-29 "Big Stink", one of the observation planes that accompanied the Nagasaki weapon delivery bomber "Bockscar". Due to the belated permission, "Big Stink" missed its rendezvous with the bomber at Nagasaki. They saw the Nagasaki detonation from the air at a distance. As the leading expert on the effects of nuclear weapons, Penney was a member of the team of scientists and military analysts who entered Hiroshima and Nagasaki following the Japanese surrender on 15 August 1945 to assess the effects of nuclear weapons.