Any of a series of U.S. liquid-fueled rockets originally developed as intercontinental ballistic missiles ( ICBM s) but also used as space launch vehicles .
Titan I missiles (used 196265), designed to deliver a four-megaton nuclear warhead over 5,000 mi (8,000 km) to targets in the former Soviet Union, were stored in underground silos but had to be raised to ground level and fueled for launch. By 1965 they had been replaced by the much larger Titan II, which could be launched directly from its silo. With a nine-megaton warhead, Titan II was the principal weapon in the land-based U.S. nuclear arsenal until the 1980s, when it was replaced by solid-fueled ICBMs (e.g., Minuteman missile s). NASA used the Titan II to launch Gemini spacecraft in the 1960s; deactivated Titan II missiles refurbished as space launchers continued to be used into the 21st century. The Titan IV, developed in the late 1980s, has larger engines to lift heavy space cargo such as that carried by the space shuttle . Coupled with the Centaur upper-stage vehicle, it is the largest and most powerful expendable launch vehicle in the U.S.