An opposing force (alternatively enemy force, abbreviated OPFOR) is a military unit tasked with representing an enemy, usually for training purposes in war game scenarios. The related concept of aggressor squadron is used by some air forces. The United States maintains the Fort Irwin National Training Center with the 11th Armored Cavalry Regiment serving in the OPFOR role. Fort Polk's Joint Readiness Training Center (JRTC) is another major training site typically reserved for light infantry units, and the OPFOR are the 1st of the 509th Airborne Infantry Regiment. The Army's Joint Maneuver Readiness Center (JMRC, at Hohenfels, Bavaria, Germany) has the 1st of the 4th Infantry Regiment as their OPFOR. Other major units include the First United States Army which consists of 16 training brigad