HMS Thetis (N25)

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HMS Thetis (N25) was a Group 1 T-class submarine of the Royal Navy which sank on 1 June 1939 with the loss of 99 lives. The submarine was salvaged, repaired and recomissioned as Thunderbolt, subsequently sunk with all hands on March 14, 1943.^[1]

She was built by Cammell Laird in Birkenhead, England and launched on June 29, 1938.

Trials were delayed because the forward hydroplanes jammed, but eventually started in Liverpool Bay under Lieutenant-Commander Guy Bolus. The first dive was attempted on June 1, 1939 at about 14:00. The submarine was too light to dive, so a survey of the water in the various tanks on board was made. One of the checks was whether the internal torpedo tubes were flooded.

Lieutenant Frederick Woods, the torpedo officer, opened the test cocks on the tubes. Unfortunately, the test cock on tube number 5 was blocked by some enamel paint and so no water flowed out even though the bow cap was open. This combined with a confusing layout of the bow cap indicators - they were arranged in a vertical line with 5 at the bottom - 1,2,3,4,6, and then 5; and the shut position for tube 5 on the dial was in a different position to the other torpedo tubes - led to the inner door of the tube being opened. The inrush of water caused the bow of the submarine to sink to the seabed 150 feet below the surface.

Although the stern remained on the surface, only four crew escaped before the rest were overcome by carbon dioxide poisoning caused by the crowded conditions, the increased atmospheric pressure and a delay of 20 hours before the evacuation started. Ninety-nine lives were lost in the incident; as well as the normal crew of 53, there were 26 Cammell Laird employees, another 9 naval officers, 4 Vickers-Armstrong employees and 2 caterers. The crew waited before abandoning the vessel until it had been discovered by Brazen, a destroyer which had been sent to search for it and which indicated her presence by dropping small explosive charges into the water.

The incident attracted legal action from one of the widows, who brought a claim of negligence against the shipbuilders, for not removing the material blocking the valve.^[2] Unfortunately for her the Admiralty successfully invoked Crown Privilige (now termed Public Interest Immunity) and blocked the disclosure of the submarine's blueprints as evidence in court, on the basis that to do so would be detrimental to national security. The case is one of interest in English law, as the judges in this case accepted the Admiralty's claim on face value with no scrutiny, a ruling later overturned.

One further fatality occurred during salvage operations, when Diver Petty Officer Henry Otho Perdue died from "the bends" on 23 August 1939. Sunday 3rd. September saw Thetis intentionally grounded ashore at Moelfre Bay, Anglesey. It was the same day that war was declared. Human remains that had not already been removed by the salvage team were now brought out to a Naval funeral, with full honours.

The submarine was successfully salvaged and repaired, being commissioned as Thunderbolt. The torpedo tubes on British submarines were afterwards equipped with a Thetis clip, one of the modifications introduced as a result of the accident. 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.

These unfortunate events mean that HMS Thetis (N25) is possibly the only military vessel in history to have claimed the lives of two crews instead of the usual one.

[edit] General characteristics

Displacement: 1,290 tons surfaced, 1,560 tons dived
Length: 276.5 ft (84 m)
Beam: 25.5 ft (7.8 m)
Draft: 14 ft 7 in (4.4 m)
Complement: 53 men
Armament:
- Ten 21 inch (533 mm) torpedo tubes - 8 internal, 2 external, all facing forward;
- 4 inch (102 mm) gun