Archaeologists Discover Manhattan Project–Era Artifacts During Excavations
Los Alamos National Laboratory archaeologists recently conducted excavations at the historic Gun Site testing range and uncovered nearly 500 previously unrecorded artifacts. This is the very site where non-nuclear parts for Little Boy and Thin Man, the gun-style bombs built as part of the Manhattan Project, were tested during World War II.
The firing range consisted of two cannon emplacements — naval gun barrels that fired explosive projectiles. Steel targets were placed at a distance of about 6 meters, and behind the guns and targets were sand traps to collect the projectiles. The purpose of the tests was to check the internal operation of the guns and subsequently refine the designs of Little Boy and Thin Man.
The plutonium Thin Man bomb — a failed gun-type plutonium weapon — was never completed because a high content of Pu‑240 in the charge which undergoes spontaneous fission by fast neutrons could lead to spontaneous detonation. This discovery led to a shift in focus to the Fat Man bomb, in which plutonium was used in a more predictable implosion-type device.
After the conclusion of the Manhattan Project, the Gun Site firing range was cleared, and the naval guns were buried.
Artifacts discovered during the excavations include fragments of rails used to move the gun enclosures, cables that transmitted data from the range to the laboratory headquarters, about a dozen projectiles, and a fragment of a steel target, which still shows an indentation from a projectile strike.
The team responsible for preserving the discovered artifacts is currently documenting details — including their physical descriptions, locations, and historical significance. They also hope to excavate and decontaminate any found weapon and then place it at reconstructed firing positions on-site, under a specially built protective shelter.