Titan I Missile System Upgrades
The first missile to undergo extensive modification was the Titan. Throughout the late 1950s the Air Force Ballistic Missile Division (AFBMD) searched for a way to remedy the two major weaknesses that plagued its first generation ICBMs: cryogenic (liquid oxygen) propellant and radio-inertial guidance.
Searching for a fuel alternative, in January 1959 the AFBMD learned that with minor modifications, Titan I could use a noncryogenic oxidizer (nitrogen tetroxide) and a storable fuel that was a mixture of hydrazine and unsymmetrical dimethylhydrazine. The benefits of the new propellant were threefold. First, because the fuel and oxidizer could be stored onboard, the missile could be kept in a constant state of readiness and fired within a minute or two. Second, the new propellant would markedly reduce the chances of a calamitous in-silo explosion such as the ones that had already destroyed two Titan I silos. Third, the new propellant would make it possible to launch the missile from inside its underground silo, thereby reducing its vulnerability to attack.
Several months later, the Air Force decided that, beginning in October 1962, it would equip all of its Titan missiles with all-inertial guidance systems. Shortly thereafter, the AFBMD proposed incorporating both changes (storable, noncryogenic propellant, and all-inertial guidance) into a new ICBM called Titan II.