Utmost spent most of her career operating in the Mediterranean, where she sank the Italian merchants Capo Vita, Enrico Costa, and Frederico C., and the German tanker Languste and also damaged the Italian merchant Manfredo Camperio.

Utmost also attacked a convoy of five German merchants and three Italian destroyers and torpedoed and sunk the German merchant Heraklea and torpedoed and damaged Ruhr.

Utmost went on to destroy the (already grounded and damaged) Italian merchant Marigola, and together with her sister, since transferred to the Poles, ORP Sokół, sank the Italian merchant Balilla.

The Commanding Officer received a Distinguished Service Order for a mission, which is believed to have been the landing of agents behind enemy lines.

On the 23rd she sank an enemy ship, but on 25 November 1942, during her return journey to Malta, she was located, attacked and sunk south west off Sicily by depth charges from the Italian torpedo boat Groppo.