A NASA upper-stage rocket also used as an uncrewed docking target. The Lockheed company (later Lockheed Martin) developed the rocket, 7.6 m long and 1.5 m in diameter, for the US Air Force. A series of Agena rockets was launched in 1966 to provide astronauts with rendezvous and docking experience. That year Gemini 8, commanded by Neil Armstrong, was the first to attempt and accomplish this.