Continuity mistake: In a scene supposed to be after the ship has been fitted with radar, it is shown entering harbour with the 'lantern' removed and the aerial covered, which is how it's shown before the ship has the radar fitted.
The Cruel Sea (1953)
1 continuity mistake
Directed by: Charles Frend
Starring: Denholm Elliott, Jack Hawkins, Donald Sinden, John Stratton
Revealing mistake: In various scenes before the Compass Rose is supposed to be fitted with radar, it's obvious the 'lantern' round the already fitted radar aerial has been removed and the aerial itself covered with a tarpaulin to simulate the ship in its earlier, pre-radar, state.