HMS UTMOST operated most successfully as part of the 10th Submarine Flotilla based in Malta under the command of Lt Cdr Richard Cayley DSO** (q.v.).

On 17 November 1942, UTMOST (Lt J W D Coombe) sailed from Malta bound for an area off Tunisia. Six days later, she signalled that she had fired her last 3 torpedoes in a successful attack against the Italian auxiliary cruiser Barletta. In fact, the Barletta had not been hit but had counterattacked with 3 depth charges. UTMOST may have mistaken the explosions for torpedo hits.

The Italian escort Groppo accompanying Barletta was detached and spent the next 20 hours searching for the submarine, without result. Two days later, Groppo attention was drawn to a position some 2 miles from the convoy when an aircraft escorting the ships dropped a bomb on what it reported as a submarine contact. Groppo gained sonar contact and attacked. This attack was deemed successful, and UTMOST was lost with all hands.