What is now Idaho National Laboratory in southeastern Idaho began its life as a U.S. government artillery test range in the 1940s. Shortly after the Japanese attacked Pearl Harbor, the U.S. military needed a safe location for performing maintenance on the Navy's most powerful turreted guns. The guns were brought in via rail to near Pocatello, Idaho, to be re-sleeved, rifled and tested. As the Navy began to focus on post-World War II and Cold War threats, the types of projects worked on in the Idaho desert changed, too. Perhaps the most well-known was the building of the prototype reactor for the world's first nuclear-powered submarine, the USS Nautilus.