On 23 January 1960, the Swiss-designed Trieste, originally built in Italy and acquired by the U.S. Navy, supported by the USS Wandank (ATF 204) and escorted by the USS Lewis (DE 535), descended to the ocean floor in the trench manned by Jacques Piccard (who co-designed the submersible along with his father, Auguste Piccard) and USN Lieutenant Don Walsh. Their crew compartment was inside a spherical pressure vessel – measuring 2.16 metres in diameter suspended beneath a buoyancy tank 18.4 metres in length[7] – which was a heavy-duty replacement (of the Italian original) built by Krupp Steel Works of Essen, Germany. The steel walls were 12.7 cm thick and designed to withstand pressure of up to 1250 kilograms per square centimetre (1210 atm; 123 MPa).[7] Their descent took almost five hours and the two men spent barely twenty minutes on the ocean floor before undertaking the three-hour-and-fifteen-minute ascent.