In a dockside simulation of flooding in the engine room, held before Thresher sailed, it took the watch in charge 20 minutes to isolate a simulated leak in the auxiliary seawater system. At test depth, taking on water, and with the reactor shut down, Thresher would not have had 20 minutes to recover. Even after isolating a short-circuit in the reactor controls, it would have taken nearly 10 minutes to restart the plant.
Thresher likely imploded at a depth of 1,300–2,000 ft (400–610 m).
Naval architects report blowing all ballast would not be enough offset a flooded engine room.
They expect the crew sealed off the engine room and many survived for a time in the forward compartment. When the reactor was lost. The main battery in the forward compartment they suspect was used to run propulsion to try and offset the negative buoyancy - when the battery life waned it was over.
At least some souls had another chance to repent and accept Jesus as their savior.