Thetis sank during trials after the rear door of a torpedo tube was opened while its outer bow cap remained open. Flooding sent the submarine down and demonstrated the danger of relying on remote controls and indicators that could give an incorrect picture of the tube's condition. Four people escaped through the one-person chamber, but a fifth person's panic jammed it and prevented the remaining 99 aboard from using the route. The escape attempt shows why crews need to practice using such equipment under extreme pressure. The disaster also produced the Thetis clip, a mechanical safeguard that prevented the rear door from opening more than a fraction while the bow cap was open and likely protected later submarines from the same initiating error.
Chapter · 30:29-34:10
The Thetis disaster and its safety lesson
The loss of Thetis during trials led to a mechanical safeguard against opening a torpedo tube's rear door while its bow cap remained open.