Bathyscaphe Trieste

The bathyscaphe Trieste
Trieste shortly after her purchase by the US Navy in 1958
Free Territory Trieste Flag.svgTrieste, Italy
Builder:Acciaierie Terni/Cantieri Riuniti dell'Adriatico
Launched:26 August 1953
Fate:Sold to the United States Navy, 1958
 United States
Reclassified:DSV-0, 1 June 1971
Fate:Preserved as an exhibit in the U.S. Navy Museum
Badge:Trieste emblem
General characteristics
Displacement:50 long tons (51 Mg)
Length:59 ft 6 in (18.14 m)
Beam:11 ft 6 in (3.51 m)
Draft:18 ft 6 in (5.64 m)

Trieste is a Swiss-designed, Italian-built deep-diving research bathyscaphe, which with its crew of two reached a record maximum depth of about 10,911 metres (35,797 ft), in the deepest known part of the Earth's oceans, the Challenger Deep, in 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.

Trieste was the first manned vessel to have reached the bottom of the Challenger Deep.[1]


General arrangement drawing, showing the main features

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 the company 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.

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 85,000 litres (22,000 US gal) 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 deck of the vessel 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. Power was provided by batteries.

Don Walsh and Jacques Piccard aboard Trieste

Trieste was subsequently fitted with a new pressure sphere,[2] manufactured by the Krupp Steel Works of Essen, Germany, in three finely-machined sections (an equatorial ring and two caps).

To withstand the enormous pressure of 1.25 metric tons per cm² (110 MPa) at the bottom of Challenger Deep, the sphere's walls were 12.7 centimetres (5.0 in) thick (it was overdesigned to withstand considerably more than the rated pressure). The sphere weighed 14.25 metric tons (31,400 pounds) in air and 8 metric tons (18,000 pounds) in water (giving it an average specific gravity of 13/(13-8) = 2.6 times that of sea water). The float was necessary because of the sphere's density: it was not possible to design a sphere large enough to hold a person that could withstand the necessary pressures, yet also 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 incompressible even at extreme pressure, thus retaining its buoyant properties and negating the need for thick, heavy walls for the float chamber.

Close-up of pressure sphere, with forward ballast silo at left

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 1,000 standard atmospheres (15,000 pounds per square inch) (100 MPa) of pressure without any modification.

9 metric tons (20,000 pounds) of magnetic iron pellets were placed on the craft as ballast, both to speed the descent and allow ascent, since the extreme water pressures would not have permitted compressed air ballast-expulsion tanks to be used at great depths. This additional weight was held in place at the throats of two hopper-like ballast silos by electromagnets, so in case of an electrical failure the bathyscaphe would automatically rise to the surface.

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.[3]

23 January 1960: Trieste just before the record dive. The destroyer escort USS Lewis is in the background.
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