and could be launched more quickly. The Martin company received a contract for the new missile, designated SM-68B Titan II, in June 1960. The Titan II was 50% heavier than the Titan I, with a longer first stage and a larger diameter second stage. The Titan II also used storable propellants: Aerozine 50 fuel, which is a 1:1 mixture of hydrazine and unsymmetrical dimethylhydrazine (UDMH), and dinitrogen tetroxide oxidiser. The Titan I, whose liquid oxygen oxidizer had to be loaded immediately before launching, had to be raised from its silo and fueled before launch. The use of storable propellants enabled the Titan II to be launched within 60 seconds directly from within its silo. Their hypergolic nature made them dangerous to handle; a leak could (and did) lead to explosions, and the fuel was highly toxic. However, it allowed for a much simpler and more trouble-free engine system than on cryogenic propellant boosters. The first flight of the Titan II was in March 1962 and the missile, now designated LGM-25C, reached initial operating capability in October 1963. The Titan II contained one W-53 nuclear warhead in a Mark 6 re-entry vehicle with a range of . The W-53 had a yield of 9 megatons. This warhead was guided to its target using an inertial guidance unit. The 54 deployed Titan IIs formed the backbone of America's strategic deterrent force until the LGM-30 Minuteman ICBM was deployed en masse during the early to mid-1960s. Twelve Titan IIs were flown in NASA's Gemini crewed space program in the mid-1960s. The Department of Defense predicted that a Titan II missile could eventually carry a warhead with a 35 megaton yield, based on projected improvements. However, that warhead was never developed or deployed. This would have made this warhead one of the most powerful ever, with almost double the power-to-weight ratio of the B41 nuclear bomb. Launch history and development The first Titan II launch, Missile N-2, was carried out on 16 March 1962 from LC-16 at Cape Canaveral and performed extremely well, flying downrange and depositing its reentry vehicle in the Ascension splash net. There was only one problem: a high rate of longitudinal vibrations during first stage burn. While this did not affect missile launches for the Air Force, NASA officials were concerned that this phenomenon would be harmful to astronauts on a crewed Gemini flight. The second launch, Missile N-1, lifted