HMS X1: The Submarine Built to Be a Battleship

Laid Down at Chatham in Secrecy

HMS X1 was built at HM Dockyard, Chatham, laid down on 2 November 1921 and completed on 23 September 1925, commissioning that December as, at the time, the largest submarine in the world. She was conceived as a submersible commerce raider, a radical concept for a submarine, designed to overpower the escorts of enemy shipping using heavy gun armament rather than relying purely on torpedoes.

Her construction was shrouded in deliberate secrecy, not least because the 1922 Washington Naval Treaty had prohibited the use of submarines against merchant vessels, making her intended role a truly awkward one to acknowledge publicly.

A Submarine Built Like a Cruiser

X1 carried four QF 5.2-inch guns mounted in twin unarmoured turrets with a range of 16,000 yards, an extraordinary armament for any submarine, alongside six 21-inch bow torpedo tubes with one reload torpedo apiece. Operating her main armament required a crew of 58 for the guns alone, a remarkably enormous commitment of manpower for what was still, fundamentally, meant to function as a stealthy vessel.

Defeated by Her Own Engines

X1's career was dogged from the start by persistent diesel engine troubles. Her starboard camshaft driveshaft fractured in January 1928, and the port shaft failed in the same way that April, while her ammunition hoists proved troublesome enough to prevent the rate of fire her design had promised.

Commanding officers who served aboard her during her Mediterranean deployment reported that she suffered from overcrowding with auxiliary machinery, cramped accommodation and poor ventilation, and in practice she spent more of her short career under repair than she ever spent at sea, a remarkably disappointing outcome for such an ambitious design.

A Brief, Troubled Life

HMS X1 was placed in reserve after 1930 and finally scrapped at Pembroke Dock on 12 December 1936, bringing to a close the story of an experimental submarine that had promised to be a genuine game-changer and instead became a cautionary tale about the limits of trying to combine a battleship's firepower with a submarine's stealth.