U Class: Small Patrol Submarine
The prototype of these boats was called the Undine Class and were built at Vickers, Barrow-in-Furness. Three of the prototype were built followed by twelve group 1 then 31 group 2 boats. With the exception of two, Umpire and Una , all 'U' class were built at Vickers.
The prototype boats had been built under the 1936 programme and were intended to be used for A/S training and for short patrols in European waters. With the start of WW11, design modifications were made, removing the external tubes in favour of a gun and removing the high bow resulting in a small increase in the overall length. The 1939 Emergency War Programme called for 12 Group 1 U class to be built. The boats were laid down between October 1939 and May 1940. The first, Utmost was completed in August 1940 and the last, Una in July 1941.
One of the class, Urchin, when completed, was renamed Sokol and loaned to the Polish Navy. It was returned to the RN in 1946 and renamed P97.
Vickers Armstrong diesels were fitted to all the Vickers built boats. At Chatham, Umpire had Admiralty 6 cylinder diesels and Una was fitted with 6 cylinder Paxman-Ricardo diesels.
Operating in Home and Mediterranean waters, the class, although receiving heavy losses, did account for 220,000 tons of enemy shipping and damaged 50,000 tons of merchant shipping plus several enemy warships. These included, 4 submarines, 1 damaged battleship, 2 cruisers sunk and 2 damaged, 3 destroyers sunk and 1 torpedo boat damaged.
Nine of the twelve Group 1 U class were lost. Of the Chatham boats Una survived the war but Umpire never entered it. Completed on 14 July 1941 Umpire, sailing to join an operational flotilla was accidentally rammed by the trawler Peter Rendricks on 19 July 1941 just 5 days after completion. Only 16 of the 38 crew were saved.