MCAS Yuma is currently the busiest air station in the Marine Corps, offering excellent year-round flying conditions and thousands of acres of open terrain for air-to-ground weapons ranges, and associated restricted airspace for military flight operations. During the 1960s, 70s, and early 1980s, MCAS Yuma was home to VMFAT-101, the Marine Corps' Fleet Replacement Squadron (FRS) for the F-4 Phantom II, training U.S. Marine Corps, U.S. Navy, and NATO/Allied flight crews and maintenance personnel in the F-4B, F-4J, F-4N, and F-4S. Following the transfer of VMFAT-101 to MCAS El Toro, California in the 1980s, MCAS Yuma became the principal Fleet Marine Force Pacific operating base for the AV-8B Harrier II, under the cognizance of Marine Aircraft Group 13 (MAG-13).