The Liberty Bell 7 was the capsule that flew on board a Mercury-Redstone rocket for the second U.S. manned spaceflight with Gus Grissom in 1961. This was a suborbital flight that only lasted a little over fifteen minutes and all went well until splashdown.
The hatch cover was designed to release via a small explosive device in the event of an emergency. For some reason, it was unintentionally activated shortly after the capsule landed in the ocean. Gus Grissom escaped safely (though he would later die in the Apollo 1 fire), but the capsule sank before it could be recovered.
Nearly 40 years later in 1999 it was finally recovered in 16,000 feet of water after a fourteen year private effort to find and retrieve it financed by the Discovery Channel.
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