The story of a corvette and its crew on anti-submarine duty during the Second World War. The film is very thoughtful, and quite closely based on Nicholas Monsarrat's outstanding novel of the same name, and to a lesser extent his factual account of his own experiences as a corvette officer, Three Corvettes, which in any case provided the source material for the novel.
The film stands out because it is not the usual chain of explosions and overblown heroics aimed at younger audiences, but a contemplative look at "real" people dealing with the horrors of war in the North Atlantic. We see the ship's company as their corvette finishes its fitting out and then works up before being released for active duty escorting convoys across the ocean. We see their frustration at not being able to hit back successfully at the U-boats; their worries about loved ones on shore, and what war does to relationships; we watch them grow as people as they learn about death at sea and how deal with an unseen enemy; we see them learn "how to die without wasting anybody's time" - surely an insight into the reality of war that very few other films could match; and we feel the agony of a captain forced to make a decision that may kill his own countrymen - the men he is supposed to be fighting to protect.
The acting is superb throughout, and my copy at least is very sharp and clear. Somehow, black and white seems to suit the mood of this film perfectly, because of its North Atlantic and Arctic Ocean setting, in the same way that Battle of the River Plate, set off Uruguay, could only be in colour.
For those interested in the ships, the corvette Compass Rose was in fact the Greek navy's flower-class Coreopsis; and the second ship, Saltash Castle, was a Royal Navy castle-class corvette, even though it is referred to as a frigate in the film.
One could argue forever about the "best" war film ever made, but if I had to choose one, this would be it.