Following the overthrow of the Shah, the regime of Ayatollah Khomeini cancelled most Western arms orders. Large shipments of spares were held back, including the last Tomcat built for Iran. which was embargoed and eventually turned over to the United States Navy. According to Tom Cooper, and contrary to some reports, Iranian F-14s were not sabotaged following the Shah's overthrow.[citation needed] Deteriorating relations between the U.S. and Iran led to an arms embargo being imposed on Iran, which covered parts for its western fighters and missiles. Accounts differ on the ability of the IRIAF to obtain parts and operate the F-14 or AIM-54. Some rumors suggest that a few of the missiles supplied to Iran before the revolution were sold to the Soviet Union, where they may have strongly influenced the development of the similar AA-9 'Amos' long-range air-to-air missile. Most evidence, however, would not support this claim. Intelligence reports state that the Iranians not only used their Phoenix missiles effectively in combat, but used them against agile enemy fighters as well.[citation needed] One such reported incident involves an Iranian Tomcat firing a single Phoenix missile at 4 Iraqi Mirage F1 fighters during their formation change, causing the hit and downing of all four.[citation needed] Iran apparently now also produces locally, their own upgraded version of the AIM-54 through their previous R&D on the system. Iran has also modified their Tomcats to fire the Russian R-73 air-to-air missile.