HMS Thunderbolt (N25): The Submarine Sunk Twice

Birkenhead as HMS Thetis-Built

This submarine was built by Cammell Laird at Birkenhead and launched on 29 June 1938 under the name HMS Thetis, a Group 1 T-class boat of 1,090 tons surfaced displacement. Her story is inseparable from one of the worst peacetime disasters in British submarine history, and it deserves to be told with the seriousness it demands.

The Thetis Disaster

On 1 June 1939, during dive trials in Liverpool Bay, Thetis carried 103 people aboard, her normal complement of 59 supplemented by shipyard workers and technical observers. A test cock on torpedo tube number five had been blocked by enamel paint, and confusing bow cap indicators led her torpedo officer, Lieutenant Frederick Woods, to open the tube's inner door while its outer hatch remained open to the sea.

Water flooded in and the submarine's bow sank to the seabed, 150 feet down. Only four men escaped through the aft escape chamber: Woods himself, Captain Harry Oram, Leading Stoker Walter Arnold and Fitter Frank Shaw.

The remaining 99 men, 51 crew and 48 shipyard and naval personnel, died of carbon dioxide poisoning in the trapped forward section, a catastrophic loss that shook the Royal Navy and the submarine-building industry alike.

The disaster led directly to a vital safety improvement, a device that became known as the Thetis clip, which allowed a torpedo tube's inner door to be tested safely before being fully opened, a change that has likely saved lives ever since.

Salvage and Rebirth

Thetis was salvaged by the Liverpool and Glasgow Salvage Association, though the recovery claimed a further life when a diver died of decompression sickness on 23 August 1939.

She was intentionally grounded at Traeth Bychan on Anglesey on 3 September 1939, the very day Britain declared war on Germany, before being fully repaired and recommissioned in 1940 under a new name, HMS Thunderbolt, commanded by Lieutenant Commander Cecil Crouch.

A Distinguished War

As Thunderbolt, she went on to fight with genuine distinction, sinking the Italian submarine Capitano Tarantini in the Bay of Biscay on 15 December 1940.

From late 1942 she was converted to carry manned torpedoes known as Chariots, and took part in Operation Principal against shipping at Cagliari in December 1942, and in January 1943 her Chariot teams successfully mined and sank the Italian light cruiser Ulpio Traiano and the freighter Viminale at Palermo, remarkable special operations that demanded extraordinary courage from the men who rode those torpedoes into enemy harbours.

Lost a Second Time

HMS Thunderbolt was finally sunk on 14 March 1943 off Sicily by the Italian corvette Cicogna, which detected her and delivered a fatal depth-charge attack. She went down in some 4,430 feet of water with the loss of all hands, a submarine that had already survived one of the worst disasters in the service's history only to be lost a second time in action.

Memorials to her crew, and to those lost in the original Thetis disaster, stand today in Holyhead and Birkenhead, a lasting reminder of a story that touched an extraordinary number of families not once but twice.