by Allan Shaw
In June 1939 H.M.S/m Thetis departed from Cammell Laird's Shipyard in Birkenhead to undertake delayed sea trials in Liverpool Bay.She had onboard a full ship's complement of officers and men plus a contingent of staff from the yard who were onboard to carry out the trials and effect any neccessary immediate repairs.Also on board that day were 2 civilian caterers,who provided the luncheon.A Mersey pilot was also embarked, as required by regulations,to pilot the vessel safely out of the river.The full total of souls onboard was 104,twice her normal complement.The sea trials were delayed due to a period of repair in the shipyard,following earlier trials in the Clyde which had shown up some severe defects during construction.Around five hours later,Thetis was marooned,with her bows stuck into the seabed,with both her forward compartments flooded. .A catastrophe was in the making,caused by the opening of the rear door of no.5 torpedo tube,whilst the bow door of the same tube was open to the sea.How had this happened on her first dive? Actually it was not her first dive as Thetis had been fully submerged in the trim basin at Cammell Laird's some weeks previously.As that test had gone o.k. the bow door(cap) must have been closed at that time as it would have produced effects which would have been noticed during the trim calculations(not least of which would have been a slight heel to starboard).Therefore the bow cap must have been opened between the trim dive and the resumed sea trials.Someone at the time,knew when the bow cap was opened,because they do not open themselves,the sea pressure tending to force the door shut against it's seating as the boat moves forward through the water.This may have been human error,or criminal negligence,we will never know.Suffice to say,many men died that day in a most appauling manner.However,one good thing came out of this tragedy,and that was the"Thetis Clip",a metal turnbuckle device fitted around the circumference of a torpedo tube rear door.In the event of simultaneous opening of both tube doors,the rear door would be held against the Thetis clips,so allowing the crew to re-close the door using the turnbuckle mechanism and a tommy bar to give the leverage required against sea pressure.Thankfully no subsequent submarines of the Royal Navy have been lost to this awful cause.Allan Shaw.
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