|Builder:||Vickers Armstrong, Barrow-in-Furness|
|Laid down:||2 November 1939|
|Launched:||20 April 1940|
|Commissioned:||17 August 1940|
|Fate:||sunk 25 November 1942|
|Length:||58.22 m (191 feet)|
|Beam:||4.90 m (16 ft 1 in)|
|Draught:||4.62 m (15 ft 2 in)|
HMS Utmost was a British U class submarine, of the second group of that class, built by Vickers Armstrong, Barrow-in-Furness. She was laid down on 2 November 1939 and was commissioned on 17 August 1940. So far she has been the only ship of the Royal Navy to bear the name Utmost.
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. An attack on another convoy made up of the German merchant Tilly L.M. Russ and the Italian merchant Cadamosto, escorted by the Italian torpedo boats Pallade and Polluce, was less successful. All torpedoes fired missed their targets.
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. Utmost later unsuccessfully attacked the Italian merchants Fabio Filzi and Siculo, as well as the Italian auxiliary minelayer Barletta. She also torpedoed and damaged the Italian cruiser Trieste.
The Commanding Officer received a Distinguished Service Order for a mission, which is believed to have been the landing of agents behind enemy lines.
Utmost left Malta for a patrol in the Mediterranean in November 1942. 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.
- Colledge, J. J.; Warlow, Ben (2006) . Ships of the Royal Navy: The Complete Record of all Fighting Ships of the Royal Navy (Rev. ed.). London: Chatham Publishing. ISBN 978-1-86176-281-8. OCLC 67375475.
- Hutchinson, Robert (2001). Jane's Submarines: War Beneath the Waves from 1776 to the Present Day. London: HarperCollins. ISBN 978-0-00-710558-8. OCLC 53783010.