The SM-68 Titan (individual variants later designated HGM-25 Titan I and LGM-25 Titan II) was the designation of two intercontinental ballistic missiles developed for the United States Air Force. The Titan I and Titan II missiles were operational between 1962 and 1987 during the Cold War. These missiles, particularly the Titan II, were the basis of the Titan family of space launch vehicles.
Titan was originally built as a backup to the SM-65 Atlas. The Titan I used RP-1 and liquid oxygen propellants and required around fifteen minutes to load the rocket and raise it to a launch position. The more powerful Titan II used nitrogen tetroxide and hydrazine, allowing it to be stored with propellant loaded, giving it a much shorter response time.