1966-10-26 USA Atlas-Centaur 9

An Atlas-Centaur 9 launch cover from "Orbit Covers", postmarked at Cape Canaveral with a machine cancel on October 26, 1966.
The Atlas-Centaur D (AC-9/174D), launched from Launch Complex 36B, successfully completed the Centaur’s first two-burn mission, placing its Surveyor spacecraft payload into geosynchronous transfer orbit. A subsequent two-burn Centaur mission, launched on April 17, 1967, sent Surveyor 3 toward the Moon for a planned lunar landing.

Atlas Centaur, the world's first space launch vehicle with a liquid hydrogen-fueled stage, suffered through a troubled development phase that lasted from 1958 to 1966. Five of the first seven test flights failed before the eighth, AC-10, successfully boosted NASA's Surveyor 1 to the Moon on 1966 May 30.

The first 12 flights were performed by Atlas Centaur LV-3C vehicles, consisting of a modified Atlas D booster topped by the Centaur LH2/LOX stage. Centaur A, B, and C variants, equipped with RL-10A-3 engines, flew during the first five missions. Beginning with the AC-6 flight, Centaur D, with RL-10A-3-1 single-burn and RL-10A-3-3 dual-burn engines, was used.

Atlas Centaur went on to become a workhorse for NASA, the Department of Defense, and commercial launch custormers. Upgraded Centaur stages were also adopted for use atop Atlas IIA, Atlas III, Atlas V, Titan IIIE, and Titan IV launchers. (Reference from ATLAS CENTAUR LV-3C DEVELOPMENT HISTORY by Ed Kyle)