The HMS Thetis Sinking

A submarine is already a coffin-shaped idea, but HMS Thetis proves how fast “routine” can become irreversible. We’re telling the story of the 1939 HMS Thetis disaster in Liverpool Bay, where a brand-new British Royal Navy T Class submarine goes down during dive trials and turns a simple systems check into a deadly cascade.

We walk through what Thetis is, how diesel electric submarines operate, and why early sea trials matter so much. Then everything hinges on details that sound harmless until they aren’t: enamel paint blocking a torpedo tube test cock, confusing bow cap indicators, and a single inner door opened to the sea. The result is immediate flooding, a steep nose-down impact on the seabed, and a packed hull with far less breathable air than anyone planned for.

Above the surface, the rescue effort stumbles in ways that are hard to believe: the escort tug drifting off station, communications delays, a search starting miles away, and precious hours slipping by even after the stern breaks the surface. Below, we track the human cost as oxygen drops, carbon dioxide rises, and hypoxia and hypercapnia strip away the ability to think clearly. We also get into the Davis escape gear attempts, the choices made topside about preserving the hull, and the long tail of lawsuits, Admiralty findings, and the safety recommendations meant to prevent another submarine sinking like this.

If you’re fascinated by naval history, submarine safety, and how small procedural failures become catastrophe, subscribe, share the show with a friend, and leave a rating or review.

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Special thank you to Lunarfall Audio for producing and doing all the heavy lifting on audio editing since April 13, 2025, the Murder of Christopher Meyer episode https://lunarfallaudio.com/

Transcript

Why Submarines Feel Like Nightmares

SPEAKER_00 0:01

There's something unnatural and terrifying about submarines. Sailing on the open ocean is terrifying enough as it is, especially in centuries past when you're at the mercy of the winds. Now, you want to get in a boat that's made to sink and travel under the water? No, thank you. Hit the wrong button, open the wrong door or hatch, and you're gonna go down quick and not be able to get back up again. Like what happened in 1939 to the HMS Tetis during its dive trials when it was sunk after both doors on one of its torpedo tubes were open to the sea and the sub inevitably sank. So, what happened? I'm Andrew, and this is History's A Disaster. Tonight we're diving into the waters of Liverpool Bay and exploring the sinking of the HMS Tetus during its dive trials in 1939. And tonight's episode is brought to you by Fantastic Chocolate, the chocolate of choice for scuba divers everywhere. During the 1930s, the British Royal Navy, fearing rising tensions with Nazi Germany, sought to replace their older submarines to counter the German U-boats that had become a major threat in World War I. So, they came up with the Triton T-Class electrical diesel submarine by 1935 and commissioned 15 to be built to start replacing the older subclasses. One of the first in the new T-Class to roll out of the Camel Lard shipyards in Birkenhead was the HMS Thetis. HMS Thetis was 275 feet long with a beam of 26.5 feet and weighed in it just over 1100 tons while surfaced and jumping up to almost 1600 tons when it dives. Gotta fat enough to go under. Being a diesel electric sub, it was powered by two 5000 horsepower diesel engines, which powered the sub and charged the batteries when it was above water, but as soon as it dives down, the sub switches over to the two 2900 horsepower electric engines for propulsion. Diesels require air to run, something that's in rather short supply under the water, necessitating the need for all electric. She was also armed with six internal torpedo tubes, four external torpedo tubes, and a four-inch deck gun. Thetis was completed and launched on June 29, 1938. And as usual for this podcast, anyways, she was fucked from the start. During a first set of sea trials in April 1939, someone put in a steering gear incorrectly so that when Thetis was turned to starboard, she actually went to port, and vice versa. During her first dive, the bile planes which controlled the rate of descent became jammed in the hard dive position and the trials had to be abandoned. One month later, her torpedo bay equipment was tested. After testing was complete, the torpedo room gear was given a good coating of enamel paint, specifically the test cock on tube number 5, which would come back to haunt the crew. But soon enough, Thetis would be ready for her next set of sea trials on June 1st. Thetis headed out along the north coast of Wales to Liverpool Bay under the command of Lieutenant Commander Guy Bolas, along with the tug Greebcock, to perform her first dive of the sea trials. On board were five officers, 48 crew, and 50 passengers, making the already cramped space even worse, since it was designed to run with a crew of 53, and most of these passengers were just along for the ride. 26 were technical advisors from Camel Lard, five other shipbuilders from different firms, seven members of the Admiralty either curious about the new sub or who would eventually be given command of one, and two caterers there to keep them all supplied with sandwiches, beer, and pies for the reception after the sea trials were over, and a mercy pilot. By 1.30 in the afternoon, Tetis was 38 miles out from Liverpool and ready to begin her first dive. Every one of the guests was given one final chance to back out and hop on the escort tug, but no one took that option. They were all ready to go quite literally down with the ship. Since no one opted to back out, Commander Bolas made the radio call that they'd be diving for three hours. But Tetis was having a little problem. Commander Bulas couldn't get it to go down. Thetis was way too light. For nearly an hour, Tetis flopped about, circling around and blowing her tanks. Just for one end of the sub to go under for a bit, before popping right back up and dropping the other end under the waves. Each time she would go just a little bit deeper, but to no avail, she just wouldn't go down. So they had to figure out why they were too light, so they ran a check on the water in different tanks aboard the sub. One of these checks was to see if the internal torpedo tubes were flooded. To check the tubes, torpedo officer Lieutenant Frederick Woods had to open the test cocks. If water came out, then the tube was flooded and you were all good to go. However, the test cock on tube number 5 had become blocked by enamel paint, which stopped any water in the tube from flowing out. Adding to this, a confusing layout on the bow cap indicators led Woods to believe the bow cap, which kept seawater from flooding into the tubes, was shut, when in fact, it was very much open. So, since no water came out of the test cock, the inner torpedo tube door was opened. Hundreds of gallons of seawater rushed into the tube, forcing its way into the sub. The sudden additional weight and the bow planes being set for hard dive forced the nose of the sub to drop rapidly. Lieutenant Woods and another crew member tried to shut the torpedo room door, but this required screwing in 18 butterfly nuts. Plus, the latch on the door was broken, which caused some difficulty getting the door shut. This would lead to the first two compartments of the sub becoming completely flooded before they could get a bulkhead door open to block the water coming in any further. Thetis, now laid down with tons of seawater in the bow, sank straight down 150 feet to the seabed. The nose of the sub slammed into the muddy bottom, bringing the sub to a sudden stop. They tried unsuccessfully to free the sub by running the engines full astern. They were stuck nose down 150 feet beneath the waves. On the surface, as the crew of the tug watched the sub struggle, a loud rush of air was heard and Thetis dropped quickly beneath the waves. Lieutenant Coulter, commander of the Greencock, knew something bad had just happened. The original plan was Thetis was supposed to settle at Periscope depth, then submerge and release smoke flares and indicator buoys. But none of that happened. Thetis just dropped out of sight beneath the waves. Coulter gave them some time, watching for any sign of the sub and thinking maybe she just surfaced elsewhere before deciding at 4.45 to send a message through to the submarine base at Gossport, but the short range of the ship to shore radio meant the message couldn't be sent directly and had to be relayed by the local telegraph office at Gossport Port. However, the boy who took messages from the harbor to the telegraph office on his bike managed to pop his tire and had to take an hour to get it fixed. It would be after 6 pm by time the message about Thetis finally made it to base. While the crew of the tug waited, they decided, you know what? Let's not drop anchor. That sounds like a great idea. Not like they're gonna drift a few miles off from where Thetis went down or anything. And of course, they didn't drift just a few miles. They ended up around four miles from where they should have been. So when naval officers in Gosport became worried about having no direct contact with Thetis for over three hours and getting the message from the tug, they immediately ordered a search of the area. The Royal Navy destroyer HMS Brazen, which was nearby in the Irish Sea, was sent to help locate the Thetis. But since the Greencock was way off course, they started the search four miles away from where they should have been. And while they searched the seas, the RAF sent out four planes to run a search of the area from the sky, looking for anything that might indicate the sun's location. While this search was being conducted four miles away, Commander Boas was getting a little worried. Normally, Tedis would carry enough air to be submerged for around 36 hours. But with the extra 50 passengers on board, this time was cut in half. They had less than 20 hours of air and the clock was ticking. They all tried to stay calm and pass the time talking about sports or what kind of reception they would get when they were finally rescued. As the air supply dwindled, they came up with a plan to help any would-be rescuers above. If they dumped most of the drinking water from the stern tanks, the stern of the Thetis should be buoyant enough to rise to the surface. And since they were only in 150 feet of water, and the Thetis was way longer than that, the stern should jet out of the water, making them easier to find and rescue. Which was a great plan. The stern broke the surface of the water and was plainly visible. However, the only problem was the search was going on 4 miles away. As time passed, with no obvious signs of rescue coming, Bolis asked for volunteers to begin the dangerous and somewhat complicated task of escaping the ship through the aft escape hatch. A slow process that would only allow two men to escape every half hour. The crew had Davis Escape Gear, a very early version of an oxygen rebreather, but few of them had been fully trained in how to use it, and of course, most of the 50 passengers on board would have no clue on how to escape a sunken sub. Captain Harry Orham, a senior fleet officer, was the first to volunteer to attempt to escape. And I say attempt because the first personnel was taking a huge risk. To get out through the escape hatch, he would have to flood it while inside to equalize the pressure before he could open the outer hatch. And with the sub tilted on such a steep angle, there was no guarantee that the outer hatch would even open properly, leading to the very real possibility he might drown in the airlock. On top of that, even if he got out, it was likely that there would only be an empty sea above to greet him, and he would most likely drown before being rescued. With surviving the escape not guaranteed, Captain Oram had messages taped to his clothes outlining the situation on board and the necessity of getting fresh air into the ship if his body was found. Meaning even in death, he could still help the remaining crew. Captain Oram and Torpedo Officer Lieutenant Woods went first, successfully making the 20-foot ascent to the surface. As night began to fall overhead, the four planes searching the seas from above spotted a gray shadow in the water and quickly found what they assumed was the sub's distress buoy. Eight of the Royal Navy's fastest destroyers left Portland in Dorset en route to the new possible location of Theetis. Following not long behind them was the salvage ship Vigilant coming out of Liverpool. The brazen was notified and diverted to the new location. As they searched through the night, checking out each possible location, they kept coming up empty-handed. By 7 o'clock the next morning, the brazen was finally at the correct location, and lookouts had finally caught sight of the stern of the Thetis sticking up 18 feet out of the water and the two men floating nearby. They were quickly picked up, and the first real news of what was going on had reached the surface. More ships were soon on scene, swarming around the exposed stern. Thick steel cables were wrapped around the stern to hold it in place, and a diver was sent down to try and connect an air hose, but the inexperienced diver only had 30 minutes of air and failed to get the hose connected in time. Sailors waited around the stern in whiteboats waiting for more to escape as the hours dragged on. Crews with cutting equipment stood ready and waiting for the order to cut through the 5-8 inch thick armor to free the men from the crippled sub. An order that would never come. Paperwork found years later would show the Admiralty intentionally held them back to preserve the hull integrity so the sub could see later use in the war they knew was coming. So basically they said, fuck the people on board, we can always get more sailors. What we really need is that sub more than we need them. On board the sub, conditions were deteriorating as the carbon dioxide built up and the oxygen had begun to run out. Desperately, Bolas ordered the men to try and escape four at a time through the escape hatch. That way they could at least get some of the men off the sub and make the remaining oxygen last just a little bit longer. However, one of the four panicked as the chamber was being filled. In his panic, he tore out his rebreather and jammed the outer hatch as he tried to open it too early. The crew inside then had to open the inner hatch and drag the four men back inside, but three of them had already drowned by time they got the hatch open. The survivor claimed that the outer hatch was now jammed and any further escape was now impossible. But two of the men decided to try their luck anyways. They said nothing's impossible, we can do this shit. And shipbuilder Frank Shaw and lead stoker Mac Arnold managed to get the jammed hatch open and made it to the surface where they were picked up by the waiting lifeboats. By now oxygen levels are dropping and carbon dioxide levels are rising dangerously, leading to hypoxia and hypercapnia as carbon dioxide built up in their bloodstream. Many of the men still aboard the sub were either already passed out or dizzy and uncoordinated from the lack of oxygen. Their ability to perform even simple tasks was going out the non-existent window as well as any hope of organizing any sort of escape. But they tried to use the escape hatch again, or at least something happened on board the sub. But whatever they tried went horribly wrong since it ended in the fetus becoming completely flooded. As tons of seawater filled the submarine, the steel cable snapped under the strain. With the loss of the steel wire holding it in place, the sub sank back down to the seabed just after midnight. On June 3rd, the news was given to nervous relatives waiting on shore. The official statement was there is no hope for the remaining men in the submarine. Within a month of the sinking, the Liverpool and Glasgow Salvage Association was brought in to salvage the sunken sub. After the operation, the Bellfronthetis was presented to the association by the Admiralty, and it was placed in the Merseyside Maritime Museum along with the plate from the number 5 torpedo tube and the officer's wardroom clock. During the salvage operations, the sinking would claim one final victim as a diver died from the Benz. On September 3rd, Tetis was intentionally grounded at Angsley the same day that war was declared. It would take nearly three weeks for the grisly task of removing the dead from the sub. In the following autopsies, it would be revealed that most of the crew died from carbon dioxide poisoning prior to the ship being flooded, and the remainder of the crew died from drowning. They would be given naval funerals with full honors. The sub would go on to be repaired and seize service as the HMS Thunderbolt under the command of Lieutenant Commander Cecil Crouch. Over the next three years, the sub would have a somewhat successful career, sinking enemy ships and disrupting shipping. Her career would come to an end on March 14, 1943, when an Italian corvette spotted her and launched death charges. The stricken Thunderbolt was sunk in over 1,300 feet in the Mediterranean Sea with the loss of all hands. The original sinking of Thetis would result in lawsuits that would drag out over the next several years. The Admiralty invoked crown privilege, which essentially blocked a lot of evidence from being brought up, and the sinking would end up after several years and multiple appeals, being ruled as a non-negligent accident, so no type of compensation was ever awarded. A tribunal was held that looked into all of the causes of the sinking. They published a report in April 1940 listing the six causes that they figured contributed to the sinking. The first cause was the rear torpedo tube door being opened when the other end was also open to the sea, allowing water to rush in. Two was the failure caused by paint blocking the test cock, which led Woods to believe the tube was not flooded. Third, the crew failed to secure the first watertight door due to the damage latch and all those stupid butterfly nuts on the door. 4. The crew failed to pump the water out of the flooded compartments, which would have been impossible to do unless they somehow managed to swim back in through the flooded compartments and close the torpedo tube bow door. Can't pump seawater out if it's just gonna keep coming back in. Fifth, the rescue attempt was less than effective, mainly stemming from Greencock's failure to anchor in place, leading the search to start some four miles away. And finally, the crew failed to save themselves. And obviously, this was the biggest one. If you can't save yourself, then why should anyone else, right? Doesn't matter that there were several other failures that would lead to this not being possible. They should have tried harder, damn it. And again, never mind that by this point they would have been severely oxygen deprived and not thinking or acting right. The inquiry lasted four years, concluding with the publication of its findings in 1943. The recommendations made by the Tribunal of Inquiry into the loss of HMS Detis were aimed at addressing the procedural failures and safety issues that contributed to the sinking with the goal of preventing similar incidents happening in the future. Recommendations that range from enhanced training on emergency procedures and equipment, stricter safety protocols during sea trials, better radios to maintain contact with the surface while a sub is submerged, improved maintenance inspections, and the development of better emergency escape mechanisms, because obviously the system they had in place was wholly inadequate to the task. On November 7th, 1947, a memorial to the crew of Thetis was unveiled at a cemetery in Hollyhead, with a second one going up on the 75th anniversary after a ceremonial wreath laying at the River Walk in Birkenhead. And that was the sinking of the HMS Thetis. Thanks for listening, and if you liked the show, please consider leaving a rating or review on your Apple Choice. And you can reach out to the show at histories of Disaster at gmail.com for questions, comments, or suggestions. Well is follow the show on social media Facebook, Instagram, TikTok, YouTube, a few others, whatever, and share the episode. Your friends will love it. And you know what? Instead of taking a ride on a submarine, get some scuba gear. For a dive, maybe with some penguins. See under the sea from a different view without a window or inches of metal between you and the majesty of life under the sea. So chase that dream. Live for today, because tomorrow is never guaranteed. Thanks and goodbye.