Jacob Beser (May 15, 1921 – June 17, 1992) 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.

Beser then studied mechanical engineering at The Johns Hopkins University, also in Baltimore, but dropped out the day after the attack on Pearl Harbor to enlist in the Army Air Forces.

[2] Because of his training and educational background, Beser was sent to Los Alamos and worked on the Manhattan Project in the area of weapons firing and fusing.

There, he met or worked with various luminaries such as Robert B. Brode, Norman Ramsey, Niels Bohr, Enrico Fermi, Edward Doll, and General Leslie Groves.

The unit began training on December 17, 1944, at the Wendover Army Air Field in Utah, before being deployed to the island of Tinian in May 1945.

Beser was the only crew member to accompany both atomic bomb missions and besides the commanding officers/pilots, had a scientific understanding of the new weapons' potential and destructiveness, as a result of his earlier high school and university education.

Lieutenant Beser was the Radar Countermeasures Officer for a combat crew of the B-29 aircraft of the 393d Bombardment Squadron, 509th Composite Group, 20th Air Force, which flew from a base in the Marianas Islands to drop on the city of Hiroshima, Japan, the first atomic bomb to be used in warfare.

Flying 1500 miles over open water to the coast of Japan, they manned their assigned positions and crossed the island of Shikoku and the Inland Sea.

They constantly faced the danger of being hit by anti-aircraft fire, enemy fighters, or suffering mechanical or other failures which would intensify the risks of carrying this powerful missile.