Each launch site had three parts, separated by at least 1,000 yards (914 m). One part (designated C) of about six acres (24,000 m²) contained the IFC (Integrated Fire Control) radar systems to detect incoming targets (acquisition and target tracking) and direct the missiles (missile tracking), along with the computer systems to plot and direct the intercept. The second part (designated L), around forty acres (160,000 m²), held 1–3 underground missile magazines each serving a group of four launch assemblies and included a safety zone. The site had a crew of 109 officers and men who ran the site continuously. One launcher would be on 15 minutes alert, two on 30 minutes and one on two hour alert. The third part was the administrative area (designated A), which was usually co-located with the IFC and contained the battery headquarters, barracks, mess, recreation hall, and motor pool. The actual configuration of the Nike sites differed depending on geography. Whenever possible the sites were placed on existing military bases or National Guard armories; otherwise land had to be purchased.