the titan iiib family emerged when the new kh-8 (gambit mark 3) photo reconnaissance satellite was being developed as the successor to the kh-7 gambit mark 1/2 which began flying in 1963. it was decided to switch to the titan family over the atlas used for kh-7 because it had substantially more lift capability and also its conventional two-stage design and hypergolic propellants made for a simpler and more reliable launch vehicle than the quirky atlas. the kh-8 was double the size of its predecessor but still well below the titan's lift capability.