The United States Air Force (USAF), four of its NATO partners, and the Pakistan Air Force (PAF), a major non-NATO US ally, are the primary operators of General Dynamics F-16 Fighting Falcon. With the evolution of sales under Foreign Military Sales (FMS) contracts, many other air forces have also acquired F-16s. Most nations that have bought F-16s continue to use them as of 2010. The F-16 is still in demand today, and many air forces are looking to replace aging inventories with F-16s. Because the USAF has steadily upgraded its F-16 inventory, it will sometimes sell older aircraft it considers obsolete as surplus Excess Defense Articles (EDAs) or as "knockdown" aircraft to supplement spares inventories. United States operators Several commands of the United States Air Force (USAF) as well as the United States Navy (USN) and National Aeronautics and Space Administration (NASA) use various models of the F-16 Fighting Falcon. United States Air Force In 2007 the USAF operated 1,245 F-16s with 701 with active forces, 490 with Air National Guard and 54 with Reserve. These were broken down to 1 F-16A Block 15, 197 F-16C/D Block 25, 350 F-16C/D Block 30, 51 F-16C/D Block 32, 222 F-16C/D Block 40, 174 F-16C/D Block 42, 198 F-16C/D Block 50, 52 F-16C/D Block 52. The USAF service branch has received a total of 2,231 F16s to its arsenal. Air Combat Command Air Combat Command (ACC) is the descendant of the merger of the Tactical Air Command (TAC) and Strategic Air Command (SAC). ACC is the primary combat aircraft operator of the United States Air Force. Originally, all new F-16s would be delivered to TAC or ACC and then transferred to other commands, but now aircraft are often delivered directly to the other commands. 20th Fighter Wing - Shaw AFB, South Carolina 55th Fighter Squadron 77th Fighter Squadron 79th Fighter Squadron 53d Wing - Eglin AFB, Florida 85th Test and Evaluation Squadron 422d Test and Evaluation Squadron, Nellis AFB, Nevada 57th Wing - Nellis AFB, Nevada 64th Aggressor Squadron United States Air Force Thunderbirds Air Education and Training Command The Air Education and Training Command (AETC) provides for most of the US Air Force's F-16 training facilities and operations. The command also provides for training of foreign air forces operating the F-16, with two squadrons providing training for Singapore and Taiwan. 54th Fighter Group (GSU) - Holloman Air Force Base 8th Fighter Squadron