It is about A Flower Class convoy escort, and had an Escort commander from PQ17 as a technical advisor.
It was a good movie and captured the flavor of the escort duties, and the seas, quite well.
It's well worth renting the DVD, with the only negative being the cheesy 50's tank ship models.
Apparently, the UK got rid of all of the corvettes quite quickly after the war, and the movie had to use HMS Coreopsis, which was being used by the Greek Navy as the Kriezis.
Some shots were claimed to be in Liverpool, but were not very recognizeable.
In the end, the only winner was the Cruel Seas....