then a Titan IV rocket would launch with an Apollo-type Service Module to rendezvous and dock. The plan required upgrading the Space Shuttle and Titan IV to use lighter aluminium-lithium alloy propellant tanks. The plan never came to fruition, but in the 1990s the Shuttle was converted to aluminum-lithium tanks to rendezvous with the highly inclined orbit of the Russian Mir Space Station. Type identification The IV A (40nA) used boosters with steel casings, the IV B (40nB) used boosters with composite casings (the SRMU). Type 401 used a Centaur 3rd stage, type 402 used an IUS 3rd stage. The other 3 types (without 3rd stages) were 403, 404, and 405: Type 403 featured no upper stage, for lower-mass payloads to higher orbits from Vandenberg. Type 404 featured no upper stage, for heavier payloads to low orbits, from Vandenberg. Type 405 featured no upper stage, for lower-mass payloads to higher-orbit from Cape Canaveral. History The Titan rocket family was established in October 1955 when the Air Force awarded the Glenn L. Martin Company (later Martin-Marietta, now part of Lockheed Martin) a contract to build an intercontinental ballistic missile (SM-68). The resulting Titan I was the nation's first two-stage ICBM and complemented the Atlas ICBM as the second underground, vertically stored, silo-based ICBM. Both stages of the Titan I used liquid oxygen and RP-1 as propellants. A subsequent version of the Titan family, the Titan II, was a two-stage evolution of the Titan I, but was much more powerful and used different propellants. Designated as LGM-25C, the Titan II was the largest missile developed for the USAF at that time. The Titan II had newly developed engines which used Aerozine 50 and nitrogen tetroxide as fuel and oxidizer in a self-igniting, hypergolic propellant combination, allowing the Titan II to be stored underground ready to launch. Titan II was the first Titan vehicle to be used as a space launcher. Development of the space launch only Titan III began in 1964, resulting in the Titan IIIA, eventually followed by the Titan IV-A and IV-B. CELV By the mid-1980s the United States government worried that the Space Shuttle, designed to launch all American payloads and replace all unmanned rockets, would not be reliable enough for military and classified missions. In 1984 Under Secretary of the Air Force and Director of the National Reconnaissance Office (NRO) Pete Aldridge decided to purchase Complementary Expendable Launch