556th Strategic Missile Squadron The 556th Strategic Missile Squadron ( 551 SMS ) is an inactive United States Air Force unit . It was last assigned to the 820th Strategic Aerospace Division , stationed at Plattsburgh AFB , New York . The 556 SMS was equipped with the SM - 65F Atlas Intercontinental ballistic missile ( ICBM ) , with a mission of nuclear deterrence . It was the only ICBM squadron east of the Mississippi River . The squadron was inactivated as part of the phaseout of the Atlas ICBM on 25 June 1965 . History . World War II . Activated as a B - 26 Marauder medium bombardment squadron in late 1942 , it trained under the Third Air Force and deployed to the European Theater of Operations ( ETO ) in July 1943 . It was initially stationed in England and assigned to IX Bomber Command . The squadron engaged in the tactical bombardment of enemy targets in Occupied Europe , initially from stations in England . After D - Day , it moved to Advanced Landing Ground s in France and Belgium , moving eastward as Allied ground forces advanced . It supported Eighth Air Force strategic bombardment missions over Nazi Germany and Occupied Europe ; striking enemy airfields to obtain maximum interference in Luftwaffe day interceptor attacks on heavy bomber formations returning to England . It also participated in the Western Allied Invasion of Germany , March – April 1945 , combat ending with the German capitation in May . The squadron became part of the United States Air Forces in Europe while demobilizing personnel in 1945 . It was reassigned to the United States as a paper unit , where it was inactivated in November 1945 . Intercontinental Ballistic Missile Squadron . Reactivated in 1957 as a Strategic Air Command ( SAC ) Strategic Missile Squadron , it initially performed testing on the SM - 62 Snark intercontinental cruise missile . It also carried out testing at the Atlantic Missile Range in Florida ; moving to Presque Isle AFB , Maine for operational deployment in 1959 . It was reactivated after the missile was brought into service . Reactivated in 1961 as a SAC SM - 65F Atlas ICBM launch squadron , the unit was stationed at Plattsburgh AFB , New York and assigned to the 820th Air ( later Strategic Aerospace ) Division on 1 July 1961 . The activation of the 556th SMA at Platsburgh AFB was the only Atlas ICBM squadron east of the Mississippi River . The squadron was assigned twelve missiles , based in a 1 x 12 configuration : twelve independent widely dispersed launch sites comprised the missile squadron . The first missile arrived in April 1962 , the silos were declared operational in December . During the Cuban missile crisis , the 556th received orders to maintain all 12 missiles on alert status . The Atlas F was the final and most advanced version of the Atlas ICBM and was stored in a vertical position inside underground concrete and steel silos . When stored , the Atlas F sat atop an elevator . If a missile was placed on alert , it was fueled with RP - 1 ( kerosene ) liquid fuel , which could be stored inside the missile for extended periods . If a decision was made to launch the missile , ít was raised to the surface and the liquid oxygen tank was filled . The launch would occur shortly after completion of this process . ( see below for site details ) . The exposure on the surface that this procedure entailed was the great weakness of the Atlas F . It was exposed and vulnerable during this time . Titan II and Minuteman missiles could be launched from within their silos , thereby eliminating this vulnerability . Also , since the Titan did not use a cryogenic fuel or oxydizer , and the Minuteman was a solid fuel rocket , they could be stored fully fueled and ready to launch within a few minutes . The first Atlas F missile was removed from alert status in favor of the more advanced LGM - 25C Titan II on December 1 , 1964 ; the squadron was inactivated on 25 June 1965 . Missile sites were subsequently sold off to private ownership after demilitarization .