I should clarify that the site is in Pocatello today. It was three miles north of Pocatello when it was built.
The Naval Ordnance Plant was commissioned in April 1942. It was a huge facility. The shop where the big 16” ship cannons were refurbished was 840 feet long and 352 feet wide. Eventually about 50 buildings were constructed on the site.
Manufacturing and refurbishing enormous guns for battleships was the main focus of the facility. Artillery needs to be refurbished after a certain number of shots are fired because the spiral grooves inside the barrel wear down. Those grooves set a projectile spinning, improving its steady trajectory.
The Pocatello plant was one of only two in the country to do this kind of work, and the only one west of the Mississippi. The site was chosen because Pocatello is far enough inland to make enemy bombardment less likely, and it was a major railroad and highway hub.
An ancillary part of the operation took place on the Arco Desert. About 50 miles northwest of Pocatello, the Navy picked a 271 square mile site from which they could test fire the big guns. It was called the Naval Proving Ground. The site contained some 27 buildings; shops, administrative operations, powder magazines, warehouses, and housing for personnel. During World War II the Navy fired most of the ordnance into the desert to the north. For a time, during the Vietnam Conflict, projectiles were aimed at the side of the Big Southern Butte. The change in targeting was due to development in the area of the original site.
The Pocatello Naval Ordnance Plant was decommissioned in the 1950s and sold. The test site on the desert became a part of what is now called the Idaho National Laboratory. Ties to the Navy remained strong there over the years as nuclear sub crews got much of their training in the Idaho desert.