Operation Retribution (German: Unternehmen Strafgericht), also known as Operation Punishment,[lower-alpha 1] was the April 1941 German bombing of Belgrade, the capital of Yugoslavia, in retaliation for the coup d'état that overthrew the government that had signed the Tripartite Pact. The bombing occurred in the first days of the German-led Axis invasion of Yugoslavia during World War II. The Royal Yugoslav Army Air Force (VVKJ) had only 77 modern fighter aircraft available to defend Belgrade against the hundreds of German fighters and bombers that struck in the first wave early on 6 April.