Rayner, D. A. The Crippled Tankerr
This rousing World War 2 tale is set in February 1943. H.M.S. destroyer HECATE is pulled out of convoy escort duty to tow the crippled (and abandoned) Greek tanker ANTIOCH 500 miles across the North Atlantic from the spot where she had been attacked by a German wolfpack to the safety of a British port. The ANTIOCH, at 14,000 tons, had been the largest ship in her convoy and her petroleum cargo is of vital importance to Britain's wartime economy. Initially angered by their rather inglorious assignment, the warship's officers and crew slowly begin to take pride in their towing assignment as they fend off (and destroy) a German U-boat and then a succession of Luftwaffe warplanes. As the ship's doctor puts it, apropos the HECATE's change of attitude towards the tanker they're towing:
"We're all bloody well balmy ... This thing - the ANTIOCH - has gotten under our skins. She's become part of us. She's a symbol of something or other. Oh, when they certify us, they'll find a word for it that none of us will understand."
With the British Isles almost within sight, an ocean-going salvage tug finally appears upon the scene and orders the HECATE to turn over the ANTIOCH. HECATE refuses. "I am ocean tug" the vessel signals to the warship. "SO AM I" is HECATE's reply, and she proceeds to bring ANTIOCH to port unassisted.
Note that the novel was published in the U.S. in 1960 under the alternate title, The Long Haul.