At the onset of the Second World War,
Triumph was a member of the 2nd Submarine Flotilla. From 26–29 August 1939, the flotilla deployed to its war bases at
Dundee and Blyth.
Home waters On 26 December 1939,
Triumph hit a German
mine in the North Sea. She lost of her
bow when it was blown off. Her pressure hull was also damaged, but her torpedoes did not detonate. She managed to limp home under the protection of fighter aircraft and destroyers, and was under repair at Chatham Dockyard until 27 September 1940.
Mediterranean Operating in the Mediterranean from early 1941,
Triumph sank the Italian merchants
Marzamemi,
Colomba Lofaro,
Ninfea,
Monrosa, the Italian auxiliary patrol vessels V 136 /
Tugnin F,
Valoroso, V 190 /
Frieda and V 137 /
Trio Frassinetti, the Italian tug
Dante de Lutti and salvage vessel , the German merchant
Luvsee, and the Greek sailing vessels
Panagiotis and
Aghia Paraskevi. She also damaged the Italian armed merchant cruiser , the Italian tankers
Ardor and
Poseidone, the Italian merchant
Sidamo and the German merchant
Norburg In June 1941 she sank the Italian submarine near northern Egypt. ==Sinking and discovery==