A spare part for Little Boy raises interesting questions

To load the bomb’s charge, an officer had to swap breech plugs — and be cool under pressure

By Micaela Hester | April 1, 2021

Little Boy Opt

When you fix a car, you need a spare tire. When you put together furniture, you may end up with extra screws. But if you were responsible for inserting charges in “Little Boy,” codename for the atomic bomb designated for Hiroshima, Japan, on Aug. 6, 1945, your spare equipment might have looked a lot like this little device.

This artifact from the Bradbury’s collection is a spare breech plug, unearthed years ago in the famed Black Hole surplus store in Los Alamos. Given the importance of its purpose, the plug’s look is deceptively simple. 

Breech plugs were necessary to charge the bomb at the right time. Morris Jeppson, the officer responsible for loading the charge in Little Boy while flying in the Enola Gay, had to remove the installed safety plugs (wooden tips painted green) and replace them with arming plugs (painted red).

Without the tell-tale red or green paint, it remains a mystery if our artifact was a spare safety or arming plug.

Swapping breech plugs was a high-pressure task. Click this link to the Atomic Heritage Foundation to check out this list of instructions prepared by Manhattan Project ordnance expert Capt. William “Deak” Parsons, who was associate director of Project Y at Los Alamos and served as the weaponeer aboard the Enola Gay during the bombing of Hiroshima.