Everyone is focusing on the controller, which I don’t think was the issue here. Also they had spare controllers.

The issue is the hull was made out of fucking fiberglass and titanium. This was the first dive since it had gone through a repair. Some tiny imperfection in that fiberglass, under thousands of pounds of pressure, and you’re fucked.

This is why real submarines are made out of steel.

On the plus side, it was probably a very quick death.