In 1972, the US Navy carried out a mission to retrieve a top-secret film capsule that sank 16,000 ft to the bottom of the ocean after it was ejected from a reconnaissance satellite. The mission was the deepest undersea salvage mission ever at the time.
CNET.com reports that the KH-9 photo reconnaissance satellite was the United State's most advanced spy satellite. It carried more than 60 miles of high-resolution photograpahic film for surveillance missions. According to CNET.com, the National Reconnaissance Office says that KH-9's 6-inch wide film frame captured a field of view of around 370 miles with a resolution of about 2 to 3 feet."
The CIA released documents pertaining to the underwater salvage mission, including photographs, on August 8. Wired.com points out that while this is not the first time the public is learning about the mission, the details of what really happened were kept secret in CIA archives for 40 years.
According to the CIA Freedom of Information Act website (CIA FOIA), the mission was carried out using the most sophisticated deep-sea submersible available to the Navy at the time, the mini-submarine Trieste II Deep Sea Vehicle or DSV-1.
Hexagon satellite system
The CIA FOIA reports that in the era before digital technology, Hexagon spy satellites returned images captured from space by dropping them in capsules over the Pacific Ocean in an area near the Hawaiian Islands. According to Space.com, Hexagon satellites, first declassified in 2011, were photo reconnaissance spacecraft that were part of the American spy program of the Cold War-era.
Reentry vehicle on ocean floor
Film stacks for the KH-9 Hexagon
The CIA FOIA website reports that on July 10, 1971, an Hexagon spy satellite attempted to return top secret package to the Earth by ejecting a capsule, the Hexagon Recovery Vehicle (Hexagon RV), over the Pacific Ocean. Wired.com reports the plan was that after the reentry vehicle opens its parachute, an aircraft would snatch it out of the sky as it descends. But the parachute failed and the reentry vehicle fell into the Pacific Ocean, hitting the water at an estimated force of 2,600 Gs. The capsule then sank 16,000 feet underwater.
According to a CIA internal memo released, "The decision was made to attempt the deep sea recovery of the RV primarily for the intelligence value of the film record and secondly to establish a capability for deep oceanographic recovery."
The planners of the mission faced the challenge of determining the point at which the capsule landed. Officials were also uncertain whether the impact damaged the capsule or whether it would still be intact after having been submerged deep under water for so long.
The mission was unprecedented at the time. According to Wired.com, the CIA report comments: "No object of this size had been actively searched for and located by sonar...[and] the Trieste II had [never] gone below 10,000 feet."
Gold film canister
Trieste II made two unsuccessful attempts to salvage the film capsule. The first attempt was on November 3, and the second on November 30, 1971. The mission was successful at the third attempt on April 25, 1972. On April 26, 1972, the Trieste returned from underwater with the Hexagon film capsule. According to the CIA document, "The third attempt was successful in locating and securing the film stacks; however, as the Trieste was surfacing, the film broke into pieces. Twenty-five feet was recovered."
Hexagon Reentry Vehicle
The Hexagon RV had also broken up when it impacted on water and film spools had spilled from the capsule. Several pieces were lost.
The CIA report says the attempt was a test of the Navy's ability to carry out deep-sea recovery missions. The report described some of the problems faced: "At the third dive, the mechanical arm failed to work, almost preventing operation of the recovery device. The on-board computer has never worked." The report recommended that "Much more attention is required to the use of high reliability parts and extensive subsystem testing to assure confidence in any given operation."
Trieste II Recovery Vehicle
Although, the CIA reports claimed that the decision to recover the RV was made primarily for the intelligence value of the film record, attention shifted, significantly, at the end of the mission from the value of the films to the opportunity afforded to test the capability of the Navy's Trieste II submersible.
The CIA report concluded: "All of the men involved remained enthusiastic and determined throughout the many frustrations and are to be commended for their fine efforts."