Bathyscaphe

By contrast, the crew cabin must withstand a huge pressure differential and is massively built.

For example, the pressure at the bottom of the Challenger Deep is more than seven times that in a standard "H-type" compressed gas cylinder.

The first bathyscaphe was dubbed FNRS-2, named after the Fonds National de la Recherche Scientifique, and built in Belgium from 1946 to 1948 by Auguste Piccard.

Piccard's second bathyscaphe was actually a third vessel Trieste, which was purchased by the United States Navy from Italy in 1957.

The crew of the Trieste, which was equipped with a powerful light, noted that the seafloor consisted of diatomaceous ooze and reported observing "some type of flatfish, resembling a sole, about 1 foot long and 6 inches across" (30 by 15 cm) lying on the seabed.