The submarine HMS Thetis was built by Cammell Laird at Birkenhead. She was laid down in December 1936 and launched in June 1938. A year later, in June 1939, three months before war began, she sank during sea trials in Liverpool Bay with ninety-nine fatalities. She was salvaged, repaired and renamed HMS Thunderbolt and commissioned in October 1940. She entered war service with considerable success but was sunk, for the second time, in March 1943 with the loss of all hands.
The accidental sinking of HMS Thetis in 1939 was, and remains, the worst peacetime loss of a submarine in British naval history. Thetis was carrying it's naval crew, other naval officials and a number of Cammell Laird personnel. The submarine carried a total of 103 men on that fateful day and only four survived. The submarine had an estimated thirty-six hours of breathable air but this was reduced by a half because of the number of personnel onboard - double its normal complement. The sinking was not without it's share of controversy. Did the Admiralty do all that they could to save the crew and official passengers as opposed to just saving the submarine? Why did she sink and why did so few survive?
The 'T' Class Submarines
Thetis was a T-class submarine and one of the first of the class to be built. Fifty-three of these diesel-electric submarines were built before and during the Second World War. They were designed to replace the older 'O', 'P' and 'R' class of submarines. They had a surface displacement of 1,290 tons, a length of just over 276 feet and a beam of just over 25 feet. Their top speed was 15.5 knots while surfaced and 9 knots when submerged. They carried a normal complement of 48 to 53 men. They carried sixteen torpedoes which could be fired through six forward torpedo tubes. In addition, they were equipped with a 4-inch quick firing deck gun.
On 1 June, 1939, the submarine, commanded by Lt Commander Guy ('Sam') Bolus, was undertaking sea trials in the Irish Sea before final acceptance procedures. Thetis was accompanied by the tug Grebe Cock. The tug's skipper was Alfred Godfrey. The tug was to standby and render any assistance necessary. On board the tug were two RN personnel, Lt Coltart and Leading Tel Crosby. At 1340, Lt Commander Bolus sent a signal to HMS Dolphin, the headquarters of the submarine service at Gosport. The signal gave his position in latitude and longitude and advised that he was about to dive the submarine. He used a megaphone to advise the skipper and the two naval men on the tug that they were about to dive. Some of the passengers and officials may have normally been expected to transfer to the attending tug. However, nobody left the submarine because they all wanted to experience the dive. Lt-Commander Bolus must have assented but this meant he had double the normal complement and they were operating in a confined space.
Thetis prepared to dive, her tanks were flooded, but she was not diving bow-first and was submerging very slowly. Something was wrong. Checks were carried out including checks to the torpedo tubes. The accident occurred when the inner door on one of the torpedo tubes was opened while the outer one was also open. The sea came rushing in and the forward two compartments were flooded. The weight of water in the forward compartments caused the boat to go into a steep dive in shallow water hitting the soft muddy seabed nose-first. They were unable to blow the main tanks and resurface. The sinking occurred at around 1500 hours.
The men on the tug realised something was wrong because she was meant to have settled at periscope depth and released smoke flares. The tug failed to anchor at the point where the submarine sank and drifted some four miles from the stricken submarine. Some reports suggest it was too deep for the tug to anchor. The water had a depth of 150 feet at this location, whereas the submarine was more than 270 feet long. It was relatively shallow water. The submarine was unable to send radio messages whilst submerged. Accordingly Lt Coltart on the tug sent a message on the radio but because of the short range of the ship-to-shore radio it had to be relayed through a telegraph office ashore. The message did not reach HMS Dolphin until 1815 hours. A search was put into effect. The destroyer HMS Brazen was nearest and was one of the first ships on the scene.
The inner torpedo tube door had been opened by Lt Frederick Woods, the torpedo officer. A test cock on the inner torpedo tube doors should have alerted him to the presence of water in the tube, but the test cocks were not functioning properly as the test cock apertures had been painted over and blocked by dried paint. When opening the cock only a trickle of water came out and so Woods thought it was safe to open the torpedo tube door. As the water gushed in, Woods and another crew member attempted to shut the door but they were unable to close it against the torrent of water. The most forward watertight compartment was evacuated but the bulkhead door could not be closed and as a result both the forward two watertight compartments were flooded causing the submarine to sink bow-first.
It soon became evident that the crew and passengers may have to escape from the submarine by way of one of two emergency escape hatches. The next morning some of the fuel and the fresh water was pumped out in the hope of getting the boat to rise. However, only the stern lifted with part of the stern section sticking out above the surface level. After dawn, the rear section of the submarine was spotted in the daylight and the rescue vessels converged on the location.
Two of the naval officers, Captain Harry Oram, not part of the crew, and Lieutenant Frederick Woods, the torpedo officer, were able to escape and reach the surface. They were picked up by boats from HMS Brazen which had just located the stricken submarine. Captain Oram was commander of the 5th Submarine Flotilla which Thetis would have joined. He and Woods volunteered to try and escape through the hatch. It was a dangerous task and few of the crew let alone the passengers had experience of using the Davis Submerged Escape Apparatus. This consisted of a nose clip, goggles and an oxygen breathing facility. The men would then enter the escape hatch, seal the door to the submarine, flood the escape chamber, and finally open the door in the hull and then ascend to the surface. Lt Cdr Bolus then ordered a second escape with four men. The more men that could escape the longer the breathable air would last. One of the four men is said to have panicked and opened the outer door too early and had damaged the hatch door. They were dragged out but three of them had drowned. A further escape effort was made by Leading Stoker Walter Arnold and Frank Shaw, a civilian, from Cammell Laird. They successfully escaped and were the last to do so. It is thought a further escape was made but something went wrong resulting in flooding. Th is caused the submarine to sink to the seabed snapping the hawsers that had been tied to the exposed stern. Only the four men referred to managed to escape from the submarine. The rest, ninety-nine men, died from carbon dioxide poisoning or drowning. Those who lost their lives included fifty-one crew members, twenty-six Cammell Laird staff, seven officials from the Admiralty, four from Vickers-Armstrong, two caterers and a Mersey harbour pilot.
After HMS Thetis had been salvaged and repaired and after completing sea trials she was commissioned in 1940 as HMS Thunderbolt under the command of Lt-Cdr Crouch. Lt Stevens was apppointed First Lieutenant. She saw service in the Atlantic and in December 1940 sank the Italian submarine Capitano Tarantini. In 1942, she was equipped with two 'chariots'. These were manned torpedoes for use against enemy ships in harbour. She and her sister submarine, HMS Trooper, wee dispatched to the Mediterranean. Their first mission was unsuccessful and Trooper was sunk. A further operation took place at Palermo in January 1943. Thunderbolt's chariots sunk an Italian light cruiser and a freighter. However, two months later, in March 1943, Thunderbolt was depth-charged by the Italian corvette Cicogna. She sank - there were no survivors.
It was a shocking tragedy, with great loss of life that occurred in the few months before the outbreak of the Second World War. There was controversy and there were suggestions of a cover up or a white-wash by the Admiralty. There were questions raised as to why the exposed rear section could not have been cut open in the period while the rear section was above the surface and before the submarine finally sank. Some felt that the Admiralty was reluctant to damage the hull in this way because they wanted to salvage the submarine - even at the risk to the lives of the men trapped aboard. War was looming and the Royal Navy needed more submarines. There were questions raised as to why it took so long to find the sunken submarine and as to why the hawsers around the after section had been insufficient to prevent the submarine from sinking to the seabed.
The remains of the ninety-nine men who lost their lives were extracted from the salvaged submarine and buried at Hollyhead on the Island of Anglesea.
HMS Thetis Secrets & Scandal (1999) David Roberts
Thetis Down - The Slow Death of a Submarine (2008) Tony Booth
Thetis Submarine Disaster (2014) David Paul
Thetis - The Admiralty Regrets (2018) C. Warren & J Benson