GSF Explorer, formerly USNS Hughes Glomar Explorer (T-AG-193), was a deep-sea drillship platform built for Project Azorian, the secret 1974 effort by the United States Central Intelligence Agency's Special Activities Division to recover the Soviet submarine K-129.

Project Azorian was a U.S. Central Intelligence Agency (CIA) project to recover the sunken Soviet submarine K-129 from the Pacific Ocean floor in 1974 using the purpose-built ship Hughes Glomar Explorer. The 1968 sinking of K-129 occurred about 1,600 miles (2,600 km) northwest of Hawaii. Project Azorian was one of the most complex, expensive, and covert intelligence operations of the Cold War at a cost of about $800 million, or $4.9 billion today.