With its return to District of Columbia control, the 121st Fighter-Interceptor Squadron was re-equipped with propeller-driven F-51H Mustangs and resumed its air defense mission of Washington, D.C. It was not until 1954, with the phaseout of the Mustang and the requirement by ADC that its interceptor squadrons be equipped with jet-powered aircraft that the squadron was upgraded to postwar-era F-86A Sabres that had been refurbished and reconditioned before being received. In August 1954, the 121st began standing daytime air defense alert at Andrews, placing two aircraft at the end of the runway with pilots in the cockpit from one hour before sunrise until one hour after sunset. This ADC alert lasted each and every day until the end of October 1958