The 851st Strategic Missile Squadron (851 SMS) is an inactive United States Air Force unit. It was last assigned to the 456th Strategic Aerospace Wing, stationed at Beale Air Force Base, California. The 851 SMS was equipped with the HGM-25A Titan I Intercontinental ballistic missile (ICBM), with a mission of nuclear deterrence. It was the last Titan I ICBM Squadron to achieve alert status on 1 February 1961. The squadron was inactivated as part of the phaseout of the Titan I ICBM on 25 March 1965.