Titan II Missile Development History
If you've already completely read the Summary, this is mostly a repeat of the development specifics. Read about the Titan I development here.
Even as the first Titan I missiles were rolling off the assembly line, the Air Force was searching for a way to modify the missile to use an oxidizer other than liquid oxygen. Searching for a way to improve the Titan I at a reasonable cost, in January 1959 the Air Force Ballistic Missile Division (AFBMD-the name was changed from WDD on June 1, 1957) found that with minor modifications Titan I could be modified to use a noncryogenic, storable propellant. That amounted to a major breakthrough, for it enabled the propellant to be stored within the missile itself, thereby permitting the Titan II to be fired in a single minute. Moreover, the new propellant made it possible to launch the missile from within the silo, simplified maintenance, and reduced the risk of accidents.
In November 1959 the Department of Defense (DOD) authorized the development of the new Titan II (SM-68B/LGM-25C) and at the same time directed that the Titan I program be discontinued after six squadrons. As planned, Titan II would be a larger, more advanced missile than its predecessor. It would be equipped with an all-inertial guidance system, a storable noncryogenic oxidizer, hypergolic fuel, and have in-silo launch capability.
In June 1960 the Air Force awarded the Martin Company the Titan II contract. Developed in parallel with the Titan I program, the Titan II took shape rapidly. Captive flight tests began in December 1961, and in February 1963 a Titan II fired from the Air Force Missile Test Center (AFMTC) in Florida logged a successful 6,500-mile flight. The following October the AFBMD's site activation task force turned over the first Titan II strategic missile wing to the Strategic Air Command (SAC). By December 1963 all six Titan II squadrons were on operational alert.