The CIA has just released an internal document kept secret for 25 years describing Project Azorian in considerable detail, though not entirely. This was the U.S operation to retrieve a sunken Soviet submarine from the Pacific Ocean. Howard Hughes' lent his name to the effort to give the United States cover. Thus the common reference to the "Hughes Glomar Explorer."
Find the full story here. At the end of this Associated Press article, there are links to the 50-page CIA document.