At the start of the 20th century, the island had become the East Coast assembly point for units being assigned to America's new overseas operations. By the onset of World War I, it had become one of the busiest recruiting stations in the country, processing 100,000 soldiers per year. From 1946 to 1949, Fort Slocum housed the headquarters of the First Air Force. In June 1949, it was renamed "Slocum Air Force Base"; this only lasted for a year before it was turned back into an Army post in June 1950. From 1955 to 1960, Fort Slocum housed Nike Ajax air-defense battery NY-15. The missiles were stored in underground silos on Hart Island with the radar and control base on Davids Island. In July 1960, after only five years of operation, Nike Battery NY-15 was closed.