Sturdy, John Rhodes "Without Convoy."

This World War 2 short story set aboard an unnamed “free” Norwegian freighter. One of the vessel’s junior officers is Rolf, who chafes at merchant marine wartime life, wishing instead to become a combat pilot in order to strike what he feels would be a real blow against the Nazi war machine. But his repeated attempts at signing up in either the U.S. Army Air Force or the R.A.F. have been rebuffed and instead he must stay with his ship. Much of Sturdy’s tale is set in the North Atlantic where Rolf’s ship, in convoy, suffers a well-described mid-ocean collision with another merchant vessel and is disabled when her steering-gear is damaged in the incident. Repairs are made, but by the time the ship is underway again she’s far out of convoy and is forced to undertake the rest of her voyage alone. All’s relatively well until, within a day’s sail from England, the ship is attacked by the Luftwaffe. Seizing the ship’s small machine gun, Rolf singlehandedly shoots one of the Nazi planes out of the skies (though not before the plane has strafed the freighter and mortally wounded her captain), and the R.A.F. soon appears on the scene to chase off the other enemy planes. Though wounded himself, Rolf realizes that he’s just been given the chance he’d hoped for: to personally take on — and vanquish — a German warplane.