HMS P33 was a Royal Navy U-class submarine built by Vickers-Armstrong at Barrow-in-Furness.

On 15 July 1941, the submarine sunk the 5,300 ton motor-vessel Barbarigo south of Punta Sciaccazza, Pantelleria, part of a small Italian convoy.

The submarine departed on her final patrol on 6 August 1941 from Malta to patrol off Sicily to intercept an Italian convoy heading towards Libya.

Her sister boat P32, which was attacking the same convoy along with HMS Unique, reported hearing a prolonged depth charge attack on 18 August and subsequently attempted unsuccessfully to contact P33.

It is, however, possible that she was sunk by the Italian torpedo boat Partenope near Pantelleria on 23 August.