HMS Unruffled was a Royal Navy U-class submarine built by Vickers-Armstrong at Barrow-in-Furness. So far she has been the only ship of the Royal Navy to bear the name Unruffled.
Unruffled spent most of her eventful wartime career in the Mediterranean, where she sank the Vichy-French merchant ship Liberia (the former Greek Cape Corso), the Italian auxiliary minesweeper N 10 / Aquila, the Italian merchant ships Leonardo Palomba,, Sant'Antioco, Citta di Catania, and Città di Spezia, the Italian tankers Castelverde and Teodolinda, the Italian sailing vessel Amabile Carolina, the Italian naval auxiliary Z 90 / Redentore, the German merchant ships Lisboa, Pommern and Baalbeck and the French tanker Henri Desprez.
On 13 October 1942 Unruffled torpedoed and sank the Italian cargo ship in the Tyrrhenian Sea off the north coast of Sicily. Loreto was carrying prisoners of war, 130 of whom were killed.
Unruffled launched unsuccessful attacks on the and the small German minesweeper R 212. Her most important target was the, which she torpedoed on 7 November 1942. Although of bow were blown off Unruffled could not sink the cruiser, having by now run out of torpedoes. The damaged cruiser was towed to port by the tug Polifemo, escorted by the torpedo boats, and . Another attack by failed, but Attilio Regolo was out of action until the Armistice of Cassibile on 8 September 1943.
As well as these actions, Unruffled took part in operations Harpoon and Vigorous. She was also the recovery vessel for Operation Principal, a chariot attack on Palermo harbour on 3 January 1943.
Unruffled survived the War and was scrapped at Troon in January 1946.