Mines Rescue Service and HMS Thetis

In response to an increasingly fragile peace in Europe the Admiralty had approved the design of and ordered over fifty new ‘Triton class’ diesel-electric submarines.

On the 1st of September 1939, the world was shaken to its core by news that Germany had invaded Poland, setting off a chain reaction that would lead to the most destructive conflict in human history.??

In the home waters of Liverpool Bay one such vessel, HMS Thetis was to make its maiden voyage diving into the cold dark waters for sea trials with 69 sailors and 34 engineers onboard, double the amount the boat was designed to carry.

Whilst attempting to dive below the water it was noted that the boat was too light preventing the manoeuvre from taking place.

A fateful decision was made to flood the torpedo tubes to gain extra weight and enable the boat to descend into the murky depths.

Unbeknown to the crew enamel paint had been used on the boats construction which had managed to block a test cock on tube number five. This safety feature would have given an indication of water being present, but because of the blockage no water flowed out – the external bow cap was open.

A confusing array of bow cap indicators numbered 2,1,4,3,6 and 5 and the ‘shut’ position mirroring the dial on tube 6 enabled a catastrophic error - the inner door of the tube was opened.

A violent ‘inrush of water’ flooded the first two compartments of the boat causing a rush of air into the other compartments and the heavy nose of the boat to dive. ??????

The alarm was raised, but it would be hours before the message would be received at Portsmouth and many hours before rescue vessels would arrive.

Carbon Dioxide (Co2)???????

This heavier than air gas is an essential part of our respiratory system - too much Co2 and not enough oxygen (O2) then we breath harder to correct the imbalance and expel Co2 on expiration along with other waste. ?

The Health and Safety Executive document ‘EH40 Workplace Exposure Limits’ tells us that the long-term exposure limit (8 hours’ time weighted average) on average is 5000 parts per million (PPM) with a short-term exposure limit (15 minutes) of 15000.

With the passing of every breath and every hour the crew would use up their remaining oxygen replacing it with Carbon Dioxide, a small number escaped, but 99 would become sleepy, lethargic until they ultimately succumbed to their fate.?

Beaching and dry dock

HMS Thetis was intentionally beached at Traeth Bychan, Anglesey and eventually placed in dry dock to facilitate the arduous task of salvage and body recovery.

The conditions onboard the HMS Thetis due to the number of bodies that had been left on board caused extreme difficulty in operating in such a dark, polluted, cramped, and claustrophobic environment.

Only one organisation had the equipment and expertise to operate in such a challenging environment.

The Mines Rescue Service

A mines rescue station was established in an old gas works at Hednesford, which would serve the collieries of Cannock Chase. A team of six men were pulled together from various teams to recover the remaining bodies from the boat.

This specialist team had available to them the ‘state of the art’ Siebe Gorman ‘Proto’ breathing apparatus, which had a long service from around 1914 through to around 1970.

Proto would potentially give them two hours of breathable air due to its ability to scrub Carbon Dioxide using ‘protosorb’ and top up oxygen using medical air in the cylinder.

?The team and their technology ultimately enable the recovery of 25 mariners and enabled a refit of the submarine, which would later be recommissioned as HMS Thunderbolt until its loss on the 14th of March 1943 with all hands.