K-129 was a Soviet submarine that sank in 1968 in the Pacific Ocean. It was a part of the Soviet Navy and was equipped with ballistic missiles. The submarine was on a patrol mission when it disappeared, leading to a significant search effort. In 1974, the CIA undertook a secret operation called Project Azorian to recover K-129. They used a specially designed ship named the Glomar Explorer to locate and retrieve parts of the submarine. The operation revealed important information about Soviet naval capabilities during the Cold War.