HMS Thetis

The Vessel

HMS Thetis was a British T-class submarine of the Royal Navy, built at the Cammell Laird yard at Birkenhead between 1936 and 1939 and launched on 29 June 1938. She was 84 metres long, 1,090 tons surfaced displacement (1,575 tons submerged), and armed with ten 21-inch torpedo tubes (six bow tubes, four external tubes) plus one 4-inch deck gun. Her propulsion was diesel-electric: two 2,500-horsepower diesel engines for surface operation and two 1,450-horsepower electric motors for submerged operation.

The T-class was the Royal Navy's standard long-range patrol submarine of the late 1930s and through the Second World War, a class of 53 boats eventually built. Thetis was the third boat of the class to be commissioned; her subsequent operational history was expected to be a standard submarine deployment pattern of the late-1930s Royal Navy: commissioning trials, fleet exercises, and operational patrols in the Atlantic and Mediterranean.

Her master on her final voyage was Lieutenant-Commander Guy Bolus, 37, an experienced career submariner. Her complement on the final voyage was 53 Royal Navy crew, 6 Cammell Laird shipyard personnel (present for trial-voyage technical observations), 2 Vickers-Armstrong armament specialists (present for torpedo-tube observations), 2 Admiralty civilian observers, 1 Admiralty's caterer, 1 Liverpool pilot, plus 38 additional observers from the shipyard and Admiralty - a total of 103 aboard, substantially beyond her design complement of 53.

The presence of 50 additional personnel aboard a submarine designed for 53 crew was a specific contributing factor to the subsequent disaster: the submarine's accommodation, ventilation, and emergency-breathing equipment were configured for her design complement, and the additional 50 personnel substantially compromised these systems.

The Voyage

HMS Thetis departed the Cammell Laird yard at Birkenhead on the morning of 1 June 1939 for her acceptance trials in Liverpool Bay, approximately 24 kilometres west of Liverpool. The planned trial programme comprised: surface running trials, submerged running trials, torpedo-tube trials (with dummy practice torpedoes rather than live weapons), and general operational shakedown.

The ship's company and the embarked civilians were briefed on the trial programme during the transit from Birkenhead to the trial area. The trial area was a standard Royal Navy trial-area approximately 25 kilometres west-southwest of Liverpool, in water depths of approximately 50 metres.

At approximately 13:15 on 1 June 1939, Thetis arrived at the trial area and prepared for submerged trials. The specific trial to be conducted was the test of her No. 5 bow torpedo tube: the inner door would be opened to confirm proper sealing, the tube would be flooded via external flooding, and a dummy practice torpedo would be discharged to confirm the tube's firing mechanism.

The specific mechanical issue relevant to the disaster was the condition of the No. 5 torpedo tube's internal drain hole. The drain hole was designed to allow seawater to enter the tube (indicating that the tube had been properly flooded and the outer door was open) before the inner door was opened; if the drain hole was obstructed, the tube would appear dry even though the outer door might have been opened and the tube was flooded.

In Thetis's case, the No. 5 torpedo tube's drain hole had been inadvertently blocked during the application of protective enamel paint to the torpedo tube's internal surfaces during the final fitting-out at Cammell Laird. The blockage was not detected during the pre-trial inspection. When the torpedo tube's outer door was opened and the inner door was subsequently opened, the tube was fully flooded but appeared from the drain hole observation to be dry.

The Disaster

At approximately 13:45 on 1 June 1939, the No. 5 torpedo tube's inner door was opened by the embarked Vickers-Armstrong armament specialist. The specialist's operational expectation was that the tube was dry; his observation of the blocked drain hole had confirmed this expectation. When the inner door was opened, however, the tube was fully flooded with seawater, and the sudden inrush of seawater under submerged pressure was uncontrollable.

The seawater entered Thetis's forward torpedo compartment at a rate of approximately 30 tonnes per minute. The specific consequence was the rapid flooding of the forward end of the submarine; her bow trimmed down; her stern rose; and within approximately three minutes, the submarine's forward third was substantially submerged below the trim angle at which her ballast-tank operations could maintain trim.

Lieutenant-Commander Bolus's immediate response was to blow ballast tanks and attempt emergency surfacing. The flooding forward, however, was substantially beyond the ballast tank's compensating capacity. HMS Thetis settled to the Liverpool Bay seabed at approximately 13:52 on 1 June 1939 in approximately 45 metres of water, her bow buried in mud and her stern approximately 10 metres above the seabed angle.

Initial rescue operations were initiated within hours: Royal Navy surface ships were sent to the location, salvage vessels were mobilised, and the submarine's position was marked by the emergency surface buoy that Bolus had released. By 02:00 on 2 June 1939, HMS Brazen and other Royal Navy destroyers had arrived on scene; HMS Vigilant and the salvage ship Ranger were dispatched from Liverpool.

The subsequent rescue operation over the following 36 hours was a catastrophic failure. The specific factors included: (i) the submarine's position at 45 metres depth was beyond the operational depth of standard Royal Navy diving equipment of 1939; (ii) the emergency breathing equipment aboard Thetis, designed for 53 personnel for 48 hours, was substantially inadequate for 103 personnel for an extended rescue period; (iii) the specific atmospheric-control procedures aboard the submarine were compromised by the substantial overcrowding; and (iv) the initial rescue attempts to cut through the submarine's hull and extract personnel failed due to the position of the submarine and the limits of 1939 salvage technology.

Four survivors escaped from Thetis through the Davis Submarine Escape Apparatus (an early breathing-apparatus system for submarine escape) between 10:00 and 16:00 on 2 June 1939. Of the 103 aboard, 99 died: suffocated by carbon dioxide buildup and progressive atmospheric degradation in the submarine's trapped air. The submarine's stern broke the surface briefly on the afternoon of 2 June 1939 (visible from the rescue ships) before finally settling to the seabed as her remaining buoyancy was lost.

The Legacy

The HMS Thetis disaster of 1-2 June 1939 was one of the worst peacetime submarine disasters in Royal Navy history and, at the time, the worst submarine disaster in world naval history. The 99 dead included 53 Royal Navy crew and 50 civilians (shipyard personnel, armament specialists, Admiralty observers), and the specific circumstances - a submarine trapped on the sea bottom for 36 hours while rescue operations failed in full view of the rescue ships - produced substantial public and parliamentary response.

The subsequent Admiralty inquiry, conducted through June and July 1939 under Admiral Sir Leonard Holden Courtney, identified the specific causes: (i) the blocked drain hole on the No. 5 torpedo tube, which had been undetected during pre-trial inspection; (ii) the inadequate pre-trial procedures that had permitted the blocked drain hole to go undetected; (iii) the excessive number of non-essential personnel embarked for the trial (50 of 103 aboard were not essential to the trial operation); (iv) the inadequate emergency-escape equipment relative to the actual complement aboard; and (v) the specific limitations of 1939 submarine rescue technology.

The specific institutional response was the comprehensive revision of Royal Navy submarine trial procedures through 1939 and 1940. The new procedures required: explicit pre-trial mechanical inspection of all hull-penetrating systems; strict limitation of non-essential personnel on trial voyages; enhanced emergency breathing equipment aboard submarines; and accelerated development of improved submarine rescue equipment. The Davis Submarine Escape Apparatus was subsequently improved through 1940-1945 based on the specific failures of the Thetis case.

The cultural response was substantial in Liverpool and the shipbuilding communities of the River Mersey. The 99 dead were predominantly Merseyside residents; multiple families lost multiple members; the Cammell Laird shipyard community was profoundly affected. The subsequent Liverpool Thetis Memorial Fund raised approximately 20,000 pounds sterling for the bereaved families and was administered for approximately 30 years.

The specific bizarre postscript of the Thetis case was her salvage and return to Royal Navy service. The submarine was raised from Liverpool Bay in September 1939 (after the outbreak of the Second World War), recommissioned as HMS Thunderbolt, and returned to active service. Thunderbolt was subsequently lost in the Mediterranean in March 1943 with all 62 crew, when depth-charged by an Italian corvette off Sicily. The ship thus claimed a total of 161 Royal Navy lives across two separate sinkings, the worst cumulative casualty record of any Royal Navy submarine.

The wreck of HMS Thunderbolt (ex-Thetis) lies at approximately 230 metres depth off Sicily; the wreck was located in 1996 and is protected under Italian cultural heritage legislation. The 99 original Thetis dead and the 62 subsequent Thunderbolt dead are commemorated by a memorial at Holyhead Cemetery, Anglesey, and by a specific memorial at Rhoscolyn on the Anglesey coast (dedicated 1988).