Inside the Nevada Test Site (NTS,) and is currently where subcritical experiments are conducted for Los Alamos and Livermore National Labs for the Stockpile Stewardship Program. U1a was originally sunk in 1968 along with another shaft for planned nuclear tests that never materialized. The Ledoux nuclear test was completed there in 1990 following the addition of a 460-foot horizontal drift to U1a. Operations were suspended until 1992, bringing the construction of U1g and additional main drift mining. Enables scientists and weapons engineers to complete multiple experiments, (also known as 'shots,') without the necessity of drilling multiple vertical shafts required of actual detonations. The drifts mined around U1a and others are considered disposable, and are used once.