Agena D was an American rocket stage used primarily during the 1960s for various space missions. It was part of the Agena family, designed to provide propulsion and support for satellites and other payloads. The Agena D variant was notable for its ability to perform orbital maneuvers, making it essential for missions involving reconnaissance and scientific research. The Agena D was launched atop various rockets, including the Atlas and Titan launch vehicles. It played a crucial role in the Cold War era, supporting military and intelligence operations. The last Agena D mission occurred in 1987, marking the end of its operational use.