Wikipedia: https://en.wikipedia.org/wiki/DSV_Alvin

Sounds like it was (shocker) really well designed. It even sank once when a cable snapped on support boat

crew escaped, and it was recovered and retrofit. And if things go sideways, the cabin/titanium sphere could detach, floating freely up to the surface.

After hearing about OceanGate, deep sea subs sounded terrifying

but reading about this is somehow very comforting.