In the end, the Titan C was never delivered, and the Air Force instead turned to "thrust augmented" Titan IIs using clustered solid-fuel rockets. These new designs, the Titan IIIs, became the DoD's main heavy-lift launch vehicle for decades afterward as it cost significantly less to manufacture and fly, in part due to using hypergolic propellants that could be stored at room temperature. An important factor in this decision was that the DoD preferred to have a launch vehicle that they were in complete control of instead of having to share the Saturn with NASA (of all Titan III/IV vehicles launched during its 40-year run, only a handful carried NASA payloads). Likewise, the development of the Titan III eliminated the need for the "flexible" staging concepts of the Saturn, which was now only intended to be used for crewed launches in the Apollo program. With the need for flexibility in launch configuration removed, most of these designs were subsequently dropped. Only the S-V survived in its original form, while the S-IV would appear in modified form and the Saturn V would feature an entirely different S-II stage.