The Imperial Iranian Air Force (IIAF) was a branch of the Imperial Iranian Armed Forces and was established by Reza Shah, the Shah of Iran, in 1920. It became operational with its first fully trained pilots on February 25, 1925. Iran's first attempt to procure aircraft from the United States in the 1920s failed due to Washington's refusal to supply equipment because of a World War I treaty. Until World War II, the IIAF's aircraft inventory consisted entirely of European aircraft, mainly British and German. However, following a co-ordinated British and Soviet invasion of Iran during World War II in response to Reza Shah's declaration of neutrality, the IIAF's bases were occupied by the Allies and all existing IIAF aircraft were either destroyed or dismantled by the Soviet and British military. A few Iranian planes did manage to get airborne during the invasion and engaged the Royal Air Force (RAF) in dogfights, in which the RAF emerged victorious.