In 1971, the KH-9 Hexagon was the United States' most advanced spy device -- a brand new photographic reconnaissance satellite as large as a school bus that carried more than 60 miles of high-resolution photographic film for surveillance missions.
The film images were sent back to Earth in recoverable return capsules. Entering the Earth's atmosphere, the canisters deployed a parachute and were then snagged by a plane in mid-air and returned to base for processing and analysis.
But in July 1971, the third reentry vehicle from the first Hexagon photo-satellite mission was lost, when the parachute broke, sending the canister into the open sea near Hawaii. The bucket sank on impact to a depth of more than 16,400 feet. This was sensitive info -- photographs of the Soviet Union's submarine bases and missile silos -- and the decision was made to attempt to recover the valuable intelligence data.
Follow the entire story here: Hexagon satellite system Pictures - CBS News.