HMS Upholder (P37) was a Royal Navy U-class submarine built by Vickers-Armstrong at Barrow-in-Furness. She was laid down on 30 October 1939, launched on 8 July 1940 by Mrs. Doris Thompson, wife of a director of the builders. The submarine was commissioned on 31 October 1940. She was one of four U-class submarines which had two external torpedo tubes at the bows in addition to the 4 internal ones fitted to all boats. They were excluded from the others because they interfered with depth-keeping at periscope depth. Career She was commanded for her entire career by Lieutenant-Commander Malcolm David Wanklyn, and became the most successful British submarine of the Second World War. After a working up period, she left for Malta on 10 December 1940 and was attached to the 10th Submarine Flotilla based there. She completed 24 patrols, sinking 93,031 tons of enemy shipping including four warships; the after the Battle of the Duisburg Convoy, two submarines (Tricheco and ) and an auxiliary minesweeper, and ten merchant ships; three troopships, six cargo ships, and an auxiliary transport. Wanklyn was awarded the Victoria Cross for a patrol in her in 1941, which included an attack on a particularly well-defended convoy on 24 May 1941 in which Upholder sank the Italian troop ship . On 28 July 1941 she damaged the (9500 tons). On 18 September 1941 she sank two troopships within hours of each other: the sister ships () and (). Upholder also damaged the German freighter Duisburg (), the French tanker Capitaine Damiani (), the Italian freighters Dandolo () and Sirio () and destroyed the wreck of the German freighter Arta () already grounded after the battle of the Tarigo Convoy. Successes Sinking Upholder was lost with all hands on her 25th patrol, which was to have been her last before she returned to England. She left for patrol on 6 April 1942 and became overdue on 14 April. On 12 April she was ordered, with and to form a patrol line to intercept a convoy, but it is not known whether she received the signal. Theories about her loss The most likely explanation for her loss is that after being spotted by a reconnaissance seaplane, she fell victim to depth charges dropped by the Italian Orsa-class torpedo boat northeast of Tripoli on 14 April 1942 in the position , although no debris was seen on the surface. The