It was 71 years ago on the 1st June that the submarine HMS Thetis sunk during a trial dive and it sadly took the lives of 99 men. The submarine was built in Birkenhead and made its way to Liverpool Bay where it was to be tested and trialed but unfortunately its first trial would be its fate. 103 men were on board in the submarine in the docks of Liverpool Bay, this was twice the number of men that it was designed to hold. Only 69 of the 103 men were sailors the rest were engineers and other men who were only helping out with its first trial. There were a number of things that went wrong that day that should have been checked. Lieutenant Frederick Woods made the decision to allow the seawater into the torpedo tubes to add weight to the submarine. But this was without the understanding and knowledge that the outer torpedo doors were already open and the tubes full of seawater. He also was unaware of the fact those weeks previous the torpedo doors has recently been painted and allowed enamel to drip inside the test tap so no water flowed out even though the bow cap was open. Prickers to clear the test cocks had been provided but they were not used. With the test tap blocked, Woods believed it was safe to open the door inside the submarine. The inrush of water caused the bow of the submarine to sink to the seabed 150 ft (46 m) below the surface. They sent a signal for help and it was received but the rescue response was not quick enough. The Conditions on board were extreme, the men were very weak due to lack of oxygen and the effects of carbon dioxide poisoning. For three days, the men had waited to be rescued, just 38 miles from shore. Just four people managed to escape. The Thetis Clip After the terrible tragedy British and Australian submarines were then equipped with a Thetis clip, one of the modifications introduced. This is a latch which allows a torpedo tube door to be opened no more than a small amount in case it is open to the sea at the bow end. Once it is clear that no flooding will occur the latch can be released and the door fully opened.