The sabotage aboard the submarine that nearly resulted in its sinking is based on the loss of the Royal Navy's in Liverpool Bay in 1939. In that case, however, the drip cock was accidentally blocked on the newly built craft by fresh paint, which led to the rear cap being opened while the bow cap was already open to the sea. Water entered at the rate of one ton per second and Thetis sank with the loss of 98 lives. In the movie, the drip cock was intentionally blocked with epoxy glue.
