Jacob Beser was a lieutenant in the United States Army Air Forces who served during World War II. Beser was the radar specialist aboard the Enola Gay on August 6, 1945, when it dropped the Little Boy atomic bomb on Hiroshima. Three days later, Beser was a crewmember aboard Bockscar when the Fat Man bomb was dropped on Nagasaki. He was the only person to have served as a strike crew member of both of the 1945 atomic bomb missions.

Bockscar, sometimes called Bock's Car, is the name of the United States Army Air Forces B-29 bomber that dropped a Fat Man nuclear weapon over the Japanese city of Nagasaki during World War II in the second – and most recent – nuclear attack in history. One of 15 Silverplate B-29s used by the 509th, Bockscar was built at the Glenn L. Martin Aircraft Plant at Bellevue, Nebraska, at what is now Offutt Air Force Base, and delivered to the United States Army Air Forces on 19 March 1945. It was assigned to the 393rd Bombardment Squadron, 509th Composite Group to Wendover Army Air Field, Utah, in April and was named after captain Frederick C. Bock.