At 9:30 a.m. on Thursday 1^st of June 1938, the H.M.S. Thetis a new submarine for the Royal British Navy sailed from Liverpool on its final sea trials. It had 106 passengers on board. At 1:40 p.m. the H.M.S. Thetis began its first ever dive the sub had planned to resurface three hours later.

At 4:00 p.m. the Thetis fired a distress flare but it was not seen.

Two hours later a search began however the Thetis's position was not discovered until early next morning. Later 4 survivors bobbed to the surface and revealed that the sub had dived with one of its torpedo tubes open.

An officer who did not know this opened the torpedo tubes inner door allowing water to flow in. Slowly the sub filled with water and sank.

It sank just before the outbreak of World War Two in those days the hull was too valuable to be wasted and was raised and rebuilt as the H.M.S. Thunderbolt.