titan 23b used the basic titan 3a core with an agena d upper stage. the titan 23b was launched from slc-4w at vandenberg afb, calif. its main payload was the gambit (kh-8 reconnaissance) satellites, although the final two 23b vehicles carried jumpseat signit satellites and had some minor upper stage modifications for them. 33 flights were made from 1966 to 1971, with one failure.