Trieste (bathyscaphe)
Trieste is a Swiss-designed, Italian-built deep-diving research bathyscaphe which reached a record depth of about in the Challenger Deep of the Mariana Trench near Guam in the Pacific. On 23 January 1960, Jacques Piccard (son of the boat's designer Auguste Piccard) and US Navy Lieutenant Don Walsh achieved the goal of Project Nekton. It was the first crewed vessel to reach the bottom of the Challenger Deep. Design. "Trieste" consisted of a float chamber filled with gasoline (petrol) for buoyancy, with a separate pressure sphere to hold the crew. This configuration (dubbed a "bathyscaphe  by the Piccards) allowed for a free dive, rather than the previous bathysphere designs in which a sphere was lowered to depth and raised again to the surface by a cable attached to a ship. Trieste" was designed by the Swiss scientist Auguste Piccard and originally built in Italy. His pressure sphere, composed of two sections, was built by Acciaierie Terni. The upper part was manufactured by the company Cantieri Riuniti dell'Adriatico, in the Free Territory of Trieste (on the border between Italy and Yugoslavia, now in Italy); hence the name chosen for the bathyscaphe. The installation of the pressure  sphere was done in the Cantiere navale di Castellammare di Stabia, near Naples. "Trieste" was launched on 26 August 1953 into the Mediterranean Sea near the Isle of Capri. The design was based on previous experience with the bathyscaphe "FNRS-2". "Trieste" was operated by the French Navy. After several years of operation in the Mediterranean Sea, the "Trieste" was purchased by the United States Navy in 1958 for $250,000 (equivalent to $ million today). At the time of Project Nekton, "Trieste" was more than 15 m (50 ft) long. The majority of this was a series of floats filled  with of gasoline, and water ballast tanks were included at either end of the vessel, as well as releasable iron ballast in two conical hoppers along the bottom, fore, and aft of the crew sphere. The crew occupied the 2.16 m (7.09 ft) pressure sphere, attached to the underside of the float and accessed from the vessel's deck by a vertical shaft that penetrated the float and continued down to the sphere hatch. The pressure sphere provided just enough room for two people. It provided completely independent life support, with a closed-circuit rebreather system similar to that used  in modern spacecraft and spacesuits: oxygen was provided from pressure cylinders, and carbon dioxide was scrubbed from breathing air by being passed through canisters of soda-lime. Batteries provided power. "Trieste" was fitted with a new pressure sphere in winter of 1958, manufactured by the Krupp Steel Works of Essen, Germany, in three finely-machined sections (an equatorial ring and two caps), and by the Ateliers de Constructions Mécaniques de Vevey. To withstand the enormous pressure of 1.25 metric tons per cm (110 MPa) at the bottom of Challenger Deep, the sphere's walls were thick (it was overdesigned to  withstand considerably more than the rated pressure). The sphere weighed in air and in water (giving it an average specific gravity of 13/(13−8) = 2.6 times that of seawater). The float was necessary because of the sphere's density: it was impossible to design a sphere large enough to hold a person that could withstand the necessary pressures and have metal walls thin enough for the sphere to be neutrally buoyant. Gasoline was chosen as the float fluid because it is less dense than water and also less compressible, thus retaining its buoyant properties and negating the need for thick , heavy walls for the float chamber. Observation of the sea outside the craft was conducted directly by eye, via a single, very tapered, cone-shaped block of acrylic glass (Plexiglas), the only transparent substance identified which would withstand the external pressure. Outside illumination for the craft was provided by quartz arc-light bulbs, which proved to be able to withstand the over (100 MPa) of pressure without any modification. Transported to the Naval Electronics Laboratory's facility in San Diego, California, "Trieste" was modified extensively by the Americans, and then used in a series of deep-submergence tests in the  Pacific Ocean during the next few years, culminating in the dive to the bottom of the Challenger Deep during January 1960. The Mariana Trench dives. "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, she reached the ocean floor in the Challenger Deep (the deepest southern part of the Mariana Trench), carrying Jacques Piccard and Don Walsh. This was the first time a vessel, crewed or uncrewed, had reached the deepest known point of the  Earth's oceans. The onboard systems indicated a depth of , although this was revised later to ; fairly recently, more accurate measurements have found Challenger Deep to be between and deep. The descent to the ocean floor took 4 hours 47 minutes at a descent rate of . After passing , one of the outer Plexiglas window panes cracked, shaking the entire vessel. The two men spent twenty minutes on the ocean floor. The temperature in the cabin was 7 °C (45 °F) at the time. While at maximum depth, Piccard and Walsh unexpectedly regained the ability to communicate with the  support ship, USS "Wandank" (ATA-204), using a sonar/hydrophone voice communications system. At a speed of almost – about five times the speed of sound in air – it took about seven seconds for a voice message to travel from the craft to the support ship and another seven seconds for answers to return. While at the bottom, Piccard and Walsh reported observing a number of sole and flounder (both flatfish). The accuracy of this observation has later been questioned and recent authorities do not recognize it as valid. The theoretical maximum depth for fish is at about , beyond which they would  become hyperosmotic. Invertebrates such as sea cucumbers, some of which potentially could be mistaken for flatfish, have been confirmed at depths of and more. Walsh later said that their original observation could be mistaken as their knowledge of biology was limited. Piccard and Walsh noted that the floor of the Challenger Deep consisted of "diatomaceous ooze". The ascent took 3 hours and 15 minutes. The National Museum of the Navy commemorated the 60th anniversary of the dive in January 2020. Other deep dives and retirement. The "Trieste" performed a number of deep dives in the Mediterranean prior to being purchased  by the U.S. Navy in 1957. It conducted 48 dives exceeding between 1953 and 1957 as the "BATISCAFO TRIESTE". Beginning in April 1963, "Trieste" was modified and used in the Atlantic Ocean to search for the missing nuclear submarine . "Trieste" was delivered to Boston Harbor by USS "Point Defiance" (LSD-31) under the command of Captain H. H. Haisten. In August 1963, "Trieste" found debris of the wreck off the coast of New England, below the surface after several dives. "Trieste"'s participation in the search earned her the Navy Unit Commendation. Following the mission, "Trieste" was returned to San Diego  and taken out of service in 1966. Between 1964 and 1966, "Trieste" was used to develop her replacement, the "Trieste II", with the original Terni pressure sphere reincorporated in her successor. In early 1980, she was transported to the Washington Navy Yard where she remains on exhibit today in the National Museum of the U.S. Navy, along with the Krupp pressure sphere.