HMS Thorn (N11) was a T-class submarine of the Royal Navy. She was laid down by Cammell Laird & Co Limited, Birkenhead and launched in March 1941.

Thorn had a short-lived career, serving in the Mediterranean.

Commencing operations in late 1941, Thorn sank the German tanker Campina, the Italian tanker Ninuccia, the Italian submarine Medusa, the Italian auxiliary patrol vessel AS 91 / Ottavia and the Italian transport ship Monviso. She also attacked an Italian convoy in the central Mediterranean, but failed to hit any ships.

On 6 August 1942 Thorn encountered the Italian torpedo boat Pegaso, escorting the steamer Istria from Benghazi, off southern Crete. Pegaso spotted an escorting aircraft machine-gunning the sea’s surface and moved in to investigate. Just four minutes after the aircraft’s attack the Pegaso picked up a sonar contact and carried out seven attacks after which contact was lost. Thorn failed to return from the patrol and is believed to have been lost in this attack. She was declared overdue on 11 August 1942.

• Colledge, J. J.; Warlow, Ben (2006) [1969]. 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.
• 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.

34°25′0″N 22°36′0″E / 34.41667°N 22.60000°E / 34.41667; 22.60000