The North Wales coast has seen many shipping disasters over the years but none more tragic than the loss of the brand new submarine HMS "Thetis" in the summer of 1939. The submarine was on her maiden voyage and 99 men died when she sank in the waters of Liverpool Bay, just 15 miles to the east of Llandudno.

Launched on 1 June 1939 from the Cammel Laird Shipyards in Birkenhead, she left for her trials/maiden voyage on the 31st of the month.

On board were 103 men, more than twice her intended complement. Just 69 were sailors, the rest being dockyard officials, engineers and technicians. It was very cramped inside that fragile hull.

The plan was for the "Thetis" to make her first dive during the trip and the civilians on board were offered the chance to leave the boat - submarines, for some reason, are always called boat, rather than ship - before the dive. All of them chose to remain on board.

The first dive attempt failed as, it was felt, the boat was too light and the decision was taken to add seawater to the torpedo tubes to make her heavier. Unbeknown to anyone the outer torpedo tube doors were already open and, therefore, the tubes were already full of water - during the painting process some weeks earlier enamel had dripped and solidified on the test tap that would and should have told Lt Frederick Woods that the doors were already open. Woods, like the rest of the men onboard, believed the tubes were empty.

The moment they began to flood the torpedo tubes, hundreds of tonnes of seawater quickly flooded into the forward compartments and the "Thetis" simply nose dived to the bottom.

It was three hours before help arrived and by that stage, the crew had already pumped out 60 tonnes of drinking water and fuel oil in an attempt to lighten her and bring her to the surface but the submarine was lying bow down with her stern protruding out of the water.

It seemed, for a while, that there was a good chance of getting the men out but vital cutting equipment arrived too late and those rescue vessels that quickly sped to the scene were literally helpless to do anything.

For 13 hours she lay, stern free of the sea with the trapped men almost within touching distance. Inside the metal hull air was running out as carbon dioxide slowly began to flood through the decks.

Lt Woods and three other sailors managed to escape using the Davis Escape gear that all submarines carried. They had squeezed through a small hatch and out into the murky water. However, when four other men tried the same route they were drowned and the escape attempts were abandoned.

A salvage ship had now appeared on the scene and a wire hawser was looped around the stern of the submarine, in an attempt to keep it raised. But with the rising tide the hawser snapped and at 3pm on 1 July the "Thetis" slipped below the surface. She did not reappear.

Rescuers were now helpless and, inevitably, the men on board became sleepier and sleepier before death finally closed in. In all, 99 men died in the tragedy. The subsequent Court of Inquiry decided that no blame could be attached to any individual and there the matter was dropped.

Shortly after the disaster war was declared on Germany and the Admiralty knew that it would soon require all the submarines it could get. As a consequence, the "Thetis" was raised from the seabed with the bodies of the sailors and dockyard workers still inside. She was beached at Traeth Bychan near Moelfre so that the men could be removed and initial investigation work carried out. Then the unlucky boat was taken back to the dockyard for repairs and modification.

The unlucky tag stuck, however. Renamed "Thunderer" she went to the Mediterranean for operations against the Italians. There, in March 1943, she was sunk in action off Sicily. This time they did not raise her again.