On January 23rd 1960, Jacques Piccard and US Navy Lieutenant Don Walsh completed Project Nekton.

Project Nekton's goal was to send a vessel into the Challenger Deep, the deepest surveyed part of the ocean in the Mariana Trench.

This was done in the bathyscaphe Trieste, which was designed by August Piccard, the father of Jacques. It reached a depth of 35,797 feet and the bottom of the Challenger Deep.

Prior to the deep dive, the vessel was of course tested with shallower, and safer, dives, before commencing with the deeper dives that culminated in the Challenger Deep dive.

By Archival Photography by Steve Nicklas, NOS, NGS (NOAA Ship Collection) [Public domain], via Wikimedia Commons (commons.wikimedia.org/wiki/File:Bathyscaphe_Trieste_Piccard-Walsh.jpg)