Completed in early 1964, Trieste II was placed on board USNS Francis X. McGraw (T-AK241) and shipped, via the Panama Canal, to Boston.

Between September 1965 and May 1966, Trieste II again underwent extensive modification and conversion at Mare Island Naval Shipyard, but there is no clear record that she was ever operated in that new configuration, i.e., the addition of skegs or outriggers on both sides of the sphere.

This work resulted in yet a new appearance for the Trieste II, and included the installation of a new pressure sphere, designed for operation to 20,000 feet (6,100 m).

Trieste II's valuable experience in deep submergence operations has helped in the design and construction of other deep-diving submersibles which could be used in rescuing crews and recovering objects from submarines in distress below levels reachable by conventional methods.

On 25 April 1972, Trieste II recovered a satellite package called a "bucket" weighing several hundred pounds from a depth of greater than 16,000 feet (4,900 m), a record at the time.