It is largely based on the sinking of the trawler Gaul which was lost with all hands in a storm in the Barents sea in 1974. Rumours abounded that the Gaul was actually on an espionage mission when she was sunk but the subsequent recovery of the wreck proved that the loss was purely accidental and the result of her offal chutes being left open during bad weather. Various incidents around the British Isles where fishing boats were dragged for miles by unidentified submarines or lost entirely also provided inspiration but it has never been resolved whether these were the responsibility of NATO or Warsaw Pact submarines.