HMS Thetis the Fated Submarine

March 2019 marks the 80th anniversary of this submarine being commissioned. Nothing unusual in that fact but this was a submarine that sunk not once but twice, along with its crew. 

On 4th of March 1939, HMS Thetis, a Group 1 T-class submarine of the Royal Navy, commenced sea trials. At that time submarine technology and its related engineering was in its infancy and there were lots of lessons to be learnt. These lessons would be learnt at a cost, which usually involved the loss of human lives. When the first submarines submerged back in the early 1900’s there were many design faults that were yet to be discovered.

Such was the case with HMS Thetis, which sank during sea trials on the 1st of June in the same year, with the loss of 99 lives. Only four survived. On board were 51 regular crew with the remaining souls made up of Admiralty overseers, training officers, two catering staff and several civilian engineers from Cammell Lairds shipyard in Birkenhead. Ironically all of the Cammell Laird’s workers were given the chance to disembark before the fateful sailing, but despite the submarine carrying almost twice the number it should, they decided to stay on-board, thus ending up in the wrong place at the wrong time.

Unfortunately it was the simple failure of one torpedo tube opening that caused the first fateful sinking. As the submarine initially struggled to submerge a torpedo officer decided to open the torpedo tubes to allow more weight to be added to the vessel. Unbeknown to the crew the tube test cock on tube No.5 was blocked by some paint enamel. This indicated there was no water in the tube even though the outer door was in fact open. In the confusion the inner door was opened and the seawater flowed through the tube and into the bow of the submarine, which became flooded. This caused the bow of the submarine to sink 150 foot below the surface to the seabed, just twelve miles off the Great Orme in Llandudno.

Little could be done other than raise the emergency through a telegram, something that took three and a half hours to reach the submarine headquarters in Portsmouth. From that point any chance of a rescue became a catalogue of errors. Mixed with the issue of the looming world war, it was felt more important to save the vessel than the lives on board. Records showing historically that the Admiralty refused to allow a rescue operation which would have to be made via the hull thus weakening the submarine and destroying chances of any future use. Only four men escaped via the submarine’s escape chamber. Due to his panic to escape the equalising waters in the chamber, the fifth man jammed open the external chamber door, essential to allow the safe use of the hatches. The four escapees pleaded in vain for the rest of the crew to be rescued. Some 26 vessels circled the submarine, all crammed with Navy personnel, salvage experts and heavy cutting equipment. However the order to move in never came and gradually the knocking from inside the submarine faded away like the lives slipping away inside it.

       The loss of life was enormous, 99 men died an agonising death due to carbon dioxide poisoning, caused by the overcrowding, increased atmospheric conditions and a delay of over twenty hours before any evacuation was attempted. Nobody other than those who escaped could envisage the horror that those condemned men must have suffered as they huddled together awaiting their fate. However human loss was not the only loss, there were also important personnel aboard; two naval constructors and several of the Cammell Laird submarine team, experienced designers and builders of submarines were lost with their skills which could have been vital to the war effort. A war that was declared on Sunday 3rd of September, the same day the submarine was intentionally grounded ashore at Traeth Bychan in Anglesey. The human remains that had not been recovered during the salvage operation lay at the bottom of the sea for almost another four months. At this time they were brought ashore with full honours, while many onlookers watched over the grim sight.

            Most of the dead were buried with full naval honours at Holyhead. Their coffins were carried through the town draped with Union Jacks. The Last Post and Reveille was played and a gun salute sounded out across the burial ceremony. Forty four of those lost were interred in a mass grave in the town which held a commemoration service in November 1947. As the event had been covered by the media, many were horrified at the way the crew were apparently left to die, ahead of World War II. Following the accident, an inquiry was held, however they failed to find out who opened the number five torpedo tube door.

            Following the recovery of HMS Thetis, the vessel was taken back to Birkenhead and following an extensive rebuild it was recommissioned in 1940 as HMS Thunderbolt. However with a new name the refurbished submarine was doomed to suffer a similar fate, although the submarine survived the trial dive and later achieved success in naval battles during the war. In 1942 the submarine was transferred to the Mediterranean alongside two sister vessels; under instruction to attack Italian military harbours destroying important supply ships in the process. HMS Thunderbolt was successful in sinking a couple of Italian ships, but was eventually sunk on 14th of March 1943 by the Italian corvette named Cicogna. HMS Thunderbolt was overwhelmed by the superior firepower of the Italian vessel, quickly sinking along with her entire crew to a depth of 4,400 feet. Bringing the total of men lost in the two disasters to almost 200.

            However, one positive to come out of the original disaster, a clip was fitted to all rear torpedo tube doors, a safety hatch that controls the opening of torpedo tubes and prevents the water from the tubes from flooding the interior of the submarine. This is still called the Thetis Clip to this day, an irreplaceable part of every British and Australian submarine but little comfort to the families who lost their men on this ill-fated submarine.


A display dedicated to the memory of HMS Thetis and the two crews who lost their lives can be seen at Holyhead Maritime Museum situated on the Anglesey Coastal Path at Holyhead.  The museum is open Tuesday to Sunday and Bank Holidays: 10am - 4pm.

Credit to Holyhead Maritime Museum for the photo