VF-121 (Fighter Squadron 121) of the US Navy was a former Pacific Fleet Replacement Air Group (RAG) unit. Originally established on 1 July 1946, as VF-781, it was redesignated as VF-121 on 4 February 1953 and disestablished on 30 September 1980. On 11 April 1958 it changed duty from Fleet Squadron to Fleet Replacement Squadron and was later charged with the training of Navy F-4 Phantom flight and maintenance crews.