I've been watching several British WWII movies and among the bunch this is the worst. It involves fictional ships and U-boats and you can clearly see that the battle scenes were shot probably in somebody's bathroom.
It was made in 1940 and it was a difficult moment for Britain, it definitely looks and feel like a propaganda movie. The main plot concerns Armitage, the captain of a British destroyer, his estranged wife Lucy and her alleged lover who happens to be assigned to Armitage's ship.
This love triangle is treated in a very sophisticated and civilised way, helped by the fact that Lucy is played by a sophisticated beauty.
In the midst of this, the Germans manage to attack the titular convoy and cause some havoc but the British keep a stiff upper lip despite the losses.