Gemini Agena target vehicle 5005 completed modification and final assembly with the installation of a number of electrical and electronic components for which it had been waiting. These included the guidance module, flight control junction box, and flight electronics package. The vehicle was transferred to test complex C-10 at Sunnyvale to begin Vehicle Systems Tests. Preliminary test tasks were completed by April 23, with preliminary inspection on April 26-27.

The Gemini 9 mission was scrubbed when the Atlas booster launched from Cape Canaveral failed to place the Gemini Agena Target Vehicle (GATV) in its planned circular orbit. A malfunction of the number 2 booster engine of the Atlas caused both the Atlas and Agena to fall into the ocean. The Gemini 9-Atlas/Agena mission was later rescheduled to 1 June using the Augmented Target Docking Adapter (ATDA).

An Air Force Titan Gemini Launch Vehicle placed the Gemini 10 (GT-10) spacecraft into orbit for the three-day mission of Astronauts John Young and Michael Collins. Rendezvous and docking were accomplished with the Gemini Agena Target Vehicle (GATV) that had been launched from Cape Kennedy aboard an Atlas Booster just ahead of GT-10. Using the GATV-10 Primary Propulsion System (PPS), the docked vehicles achieved a manned-flight altitude record of 476 miles. Reentry was accomplished on 21 July and recovery was made 544 miles east of Cape Canaveral. Space craft engaged in investigation of spaceflight techniques and technology (US Cat A).