Bockscar. Flown by Major Charles W. Sweeny, Bockscar flew out of Tinian with the Fat Man bomb loaded in its bomb bay, but, due to heavy cloud cover, anti-aircraft, and smoke from a nearby firebombing mission, was unable to drop it on the primary target of Kokura. She proceeded to her secondary target of Nagasaki, and dropped the bomb which yielded an explosion equal to 21 kilotons of TNT.

The actual plane has been fully restored to the Nagasaki mission specs and is located in the Air Force Museum in Dayton, Ohio. Which is very well worth the visit if you're ever in the area.