copied from: English submarine accidents.
1 June, 1939 - The Thetis founders after flooding through the #5 forward tube, killing a total of 99 crewmembers, civillian technicians, and senior naval observers. One observer, one officer, and two crewmembers escaped. Thetis is salvaged and recommissioned as HMS Thunderbolt. (Johnson, "Thetis Submarine") .

Congratulations to your memory, Fionn.

Wolfgang