the various depth ratings, have resulted in multiple erroneous accounts of submarines not being crushed at their crush depth. Notably, several World War II submarines reported that, due to flooding or mechanical failure, they'd gone below crush depth, before successfully resurfacing after having the failure repaired or the water pumped out. In these cases, the "crush depth" is invariably either a mistranslated official "safe" depth (i.e. the test depth, or the maximum operating depth), or the design depth, or a prior—and evidently incorrect—estimate of what the crush depth might be. World War II German U-boats of the types VII and IX generally imploded at depths of 200 to 280 metres (660 to 920 feet). See also HY-80 steel USS Thresher (SSN-593) - a submarine that likely imploded after reaching its crush depth References Pressure vessels Failure Pressure Submarine design