Auguste Piccard

On the 23rd of January 1960, two men climbed into a steel sphere and sank to the bottom of Challenger Deep.

They were Jacques Piccard, a Swiss oceanographer and engineer whose father, Auguste Piccard, had designed the vessel they were riding in, and Don Walsh, a lieutenant in the United States Navy who'd been assigned to the project as part of the Navy's Deep Submergence Programme.

The vessel was called the Trieste and it was not a submarine.

A submarine is a vessel that moves through the water under its own power, capable of navigating horizontally, diving, surfacing and manoeuvring.