hope to hell that you've got a sandbox below you before you reach crush depth, if so, all stop and hope the DD's think yoursunk, happend to me in Gibraltar, fixed her up and limped to la spezia leaking fuel everywhere
had every compartment except hydrophone room filling up, the oxygen was well into the red
other than that, all i can say is if no ground is below you, blow ballasts and reverse engines, and set your dive planes for surface, other than that... your sunk!