Building 9731 was completed March 1943. It was the first building completed on the site. It was also the first building where calutrons were installed. There were two Alpha calutrons and two Beta calutrons installed in what was known as the “Pilot Facility.” They were initially used to prove the operation of the calutrons and to provide training for the operators. The magnets of those very first calutrons installed at Y-12 are still there today.