HMS Thetis changed safeguards more than the need for trials

What changed in Royal Navy submarine trials after the loss of HMS Thetis?

A safety interlock addressed the immediate failure, but the Navy continued trials and tried to make the early stages survivable rather than abandoning demanding dive tests.

First dives are commonly kept near a dockyard or in conditions where a disabled submarine can be recovered. Thetis had passed preliminary checks before the fatal problem emerged during more advanced work, and the disaster led to design or operating changes. Testing remains necessary because the deeper hazard cannot be removed by procedure alone.