[2] The mission was the final goal for Project Nekton, a series of dives conducted by the United States Navy in the Pacific Ocean near Guam.

Since the 1980s, it has been on exhibit in the National Museum of the United States Navy in Washington, D.C. Trieste was designed by the Swiss scientist Auguste Piccard, based on his previous experience with the bathyscaphe FNRS-2.

The term bathyscaphe refers to its capacity to dive and manoeuvre untethered to a ship in contrast to a bathysphere, bathys being ancient Greek meaning "deep" and scaphe being a light, bowl-shaped boat.

[6] This general configuration remained the same but after modifications to the hull for Project Nekton, which included the dive to Challenger Deep, Trieste was more than 15 metres (49 ft) long.

The sphere was completely self-contained, having a closed-circuit rebreather system with oxygen provided from cylinders while carbon dioxide was scrubbed from the air by being passed through canisters of soda-lime.

The new sphere was also steel, but smaller at 2.16 metres (7.1 ft) diameter and with thicker walls, at 127 millimetres (5.0 in),[5] calculated to withstand the 1,250 kilograms per square centimetre (123 MPa) pressure at the bottom of Challenger Deep plus a substantial factor of safety.

Changes in the volume of the gasoline caused by any slight compression or temperature changes were accommodated by the free flow of seawater into and out of the bottom of the tanks during a dive via valves, equalising the pressure and allowing them to be lightly built.

Ballast was held in two conical hoppers fore and aft of the crew sphere each containing 9 metric tons (20,000 pounds) of iron shot.

Water tanks at each end of the hull were pumped out for flotation, lifting, and towing on the surface and fully flooded to allow sinking.

[12] Following its acquisition by the United States Navy, Trieste was modified extensively by the Naval Electronics Laboratory, San Diego, California, tested in the Pacific Ocean over the next few years, and culminated in a dive to the bottom of Challenger Deep 23 January 1960.

[6] Trieste departed San Diego on 5 October 1959 for Guam aboard the freighter Santa Maria to participate in Project Nekton, a series of very deep dives in the Mariana Trench.

On 23 January 1960, it reached the ocean floor in the Challenger Deep (the deepest southern part of the Mariana Trench), carrying Jacques Piccard and Don Walsh.