The Navy's Trieste II went to 20,000 feet (6.1 km) in the 1960s. It dove to the wreckage of the Thresher, among other things and was in service until 1980. It w

The Navy's Trieste II went to 20,000 feet (6.1 km) in the 1960s. It dove to the wreckage of the Thresher, among other things and was in service until 1980. It was replaced by Alvin-class of deep-submergence vehicles. https://en.wikipedia.org/wiki/Trieste_II_(Bathyscaphe) https://en.wikipedia.org/wiki/Trieste_II_(Bathyscaphe)