The 400th Strategic Missile Squadron (400 SMS) is an inactive United States Air Force unit. It was last assigned to the 90th Operations Group, stationed at F.E. Warren AFB, Wyoming. The 400 SMS was equipped with the LGM-118A Peacekeeper Intercontinental ballistic missile (ICBM), with a mission of nuclear deterrence. It was the only operational USAF Peacekeeper ICBM squadron. The squadron was inactivated as part of the phaseout of the Peacekeeper ICBM on 19 September 2005.