Only July 10, 1971, America's newest photo reconnaissance satellite, the KH-9 Hexagon, dropped a capsule loaded with film toward the Earth. The re-entry vehicle was supposed to open its parachute; an American aircraft would snatch it out of the sky in mid-descent. But the chute was never unfurled. The re-entry vehicle hit the Pacific Ocean with a force of approximately 2,600 G's. And then it sunk down into the deep, before settling at 16,000 feet. Shortly thereafter, officials from the U.S. Navy and the Central Intelligence Agency decided to go after the Hexagon capsule, using America's most advanced deep-sea exploration vehicle, the Trieste II. There were just two problems with the mission, an internal CIA memo noted: "No object of this size had been actively searched for and located by sonar." And "the Trieste II had not gone below 10,000 feet." While the incident has been discussed publicly before, many details of what happened next have been locked in government archives for 40 years. On Wednesday, the CIA declassified documents and photographs showing how it went after the Hexagon capsule. Here's what they showed. (Above) The Hexagon capsule -- known as Recovery Vehicle 1201-3 -- sitting at the bottom of the Pacific.

The original re-entry vehicle for the Hexagon spy satellite. First launched on June 15 of 1971 aboard a Titan II rocket, it carried 60 miles of high-resolution photographic film to snoop on the Soviets and Chinese. The satellite was declassified last year by the National Reconnaissance Organization.

A closer look at the Hexagon RV, before it was launched. American intelligence wanted a way to regularly photograph huge swaths of China and the Soviet Union. Hexagon was their answer. Using a folded camera with a 60-inch focal length, each frame shot by Hexagon could capture 370 nautical miles at a time.

A view of the Hexagon's RV's encoder. The satellite became instantly invaluable in the early '70s, writes space historian Dwayne Day. America was entering into arms negotiations with the Soviets. "Within just a few short weeks a single Hexagon spacecraft could photograph nearly the entire Soviet Union taking pictures so good that analysts working in darkened rooms back in Washington's Navy Yard could make a precise count of every single Soviet ICBM silo in operation or under construction, and identify the type."

The Hexagon RV's A1 motor drive electronics. The white lettering is the serial number.

Recovering the Hexagon's film wouldn't be easy: Rough seas and high pressure made for a hostile environment. A CIA photograph appears to show the effects of deep-sea pressure on polystyrene cups.

The Trieste II was designed to handle that kind of pressure. It could crawl along the ocean depths at two knots for up to 11 hours, hauling five tons of gear -- including a rudimentary on-board computer.

A closer look at the Trieste II and its claw, which was used to manipulate objects undersea. The recovery effort was problem-plagued even before it began. On Oct. 4, the deep-sea vessel was sent out on a trial mission, to recover a dummy capsule in 6,500 feet of water off of the coast of San Diego. It failed because of unspecified "equipment problems."

Another view of the Trieste II. The mission officially kicked off on Oct. 8, when the U.S.N.S. DeSteiger dropped a series of deep-ocean transponders that gave the Hexagon re-entry vehicle's approximate location. Those transponders wound then be used the guide the deep-sea vehicle.

The Trieste II's claw. On Nov. 21, the ship left Pearl Harbor for the crash site. Bad sea conditions and battery woes kept the vessel from diving until almost the end of the month.

Another look at the Trieste II. The mission officially kicked off on Oct. 8, when the U.S.N.S. DeSteiger dropped a series of deep-ocean transponders that gave the Hexagon re-entry vehicle's approximate location. Those transponders wound then be used the guide the deep-sea vehicle.

The Trieste II had to surface in the early hours of Dec. 1. But the crew believed they had finally spotted the first piece of debris from the spacecraft.

The Hexagon's film spools. It wasn't until April that the military and CIA could return to the crash site, and begin a second recovery effort. Mother Nature refused to cooperate, as one Agency office noted on April 24: "The weather had improved somewhat (8-10 foot seas) and though this was rougher than they had operated in before.... We recommenced preparations for the dive."

The Trieste II's divers were told a cover story: that they were looking for an instrument package from the academic Scripps Institute that was sensitive to light, and therefore had to be covered by a black shroud. On April 25, before that shroud could be dropped, divers photographed the Hexagon's film spools.

The Trieste finally recovered the giant roll of 6.6-inch-wide Kodak high-definition aerial film. The mission appeared, at long last, to be a success. "But when the Trieste surfaced, a CIA memo notes, the payload "disintegrated into a cloud of silt with a few pieces falling through the tines of the hook. Everyone went from an emotional high to an emotional low in about one millisecond."

The film broke into seven pieces. the shock of re-entry and the nine months in the brine proved too much for the film. There were no usable images on the roll. This scrap was the best of the images -- and the only tangible result from the CIA's nearly year-long rescue effort.