When the film was made in 1952, no Flower Class corvettes remained in Royal Navy service. The ship used was therefore the Greek corvette Kriezis, brought to Britain for scrapping. She was already scrapped by the time the film premiered.
Two versions were shot of the scene where Captain Ericson talks to Lieutenant Lockhart about having to blow up his own men in the water. In one version he shed one tear, and in the second version he shed two tears. The second version was used.
The Compass Rose was played by ex-HMS Coreopsis. She was given the number K49 in the film which was the number of HMS Crocus (sometimes wrongly thought to have been used in the film). The real number of the Coreopsis was K32.
On boarding the castle class frigate, Ericson and Lockhart question whether there is actually a castle called 'Saltash Castle'. There is a castle in Saltash but it is more correctly called Trematon Castle.