The Central Army Group (CENTAG) was a NATO military formation comprising four Army Corps from two NATO member nations comprising troops from Canada, West Germany and the United States. During the Cold War, CENTAG was NATO's forward defence in the southern half of the Federal Republic of Germany (FRG). The northern half of the FRG was defended by the four Army Corps of NATO's Northern Army Group (NORTHAG). During wartime, CENTAG would command four frontline corps . Air support was provided by Fourth Allied Tactical Air Force.