HMS Trenchant was a Trafalgar-class nuclear-powered fleet submarine of the Royal Navy built by Vickers Shipbuilding, Barrow-in-Furness. Trenchant was based at HMNB Devonport. She was the third vessel and the second submarine of the Royal Navy to be named for the characteristic of vigour and incisiveness.

The Trafalgar class is a class of nuclear-powered fleet submarines (SSNs) in service with the Royal Navy, and the successor to the Swiftsure class. Like the majority of Royal Navy nuclear submarines, all seven boats were constructed at Barrow-in-Furness shipyard, Cumbria. With only one boat remaining active and in commission and six retired from the seven originally in service, the class makes up part of the Royal Navy's nuclear-powered ‘hunter-killer’ submarine force. The Trafalgar class has nearly been replaced by the larger and more capable Astute class, of which five are commissioned.