The Martin Marietta SM-68A/HGM-25A Titan I was the United States' first multistage Intercontinental Ballistic Missile (ICBM). Incorporating the latest design technology when designed and manufactured, the Titan I provided an additional nuclear deterrent to complement the U.S. Air Force's SM-65 Atlas missile. It was the first in a series of Titan rockets, but was unique among them in that it used LOX and RP-1 as propellants, while the later Titan versions all used storeable fuels instead. Though the SM-68A was operational for only three years, it was an important step in building the Air Force's strategic nuclear forces.