Why The Cruel Sea feels authentic

How realistic is The Cruel Sea's depiction of life in North Atlantic convoy escorts?

Very realistic, largely because many of its writers and production personnel had served in convoy escort operations.

The Cruel Sea is rated as a highly realistic depiction of North Atlantic convoy escort service. Many people involved in writing and producing it had served in that wartime environment. Their direct experience gives the film unusual authority on convoy-escort life. The brief answer explains the source of that realism without claiming that every dramatic scene is a documentary record.