Summer 1940: Andy Holt is second mate on the SS Barranquilla, sailing from the Clyde to Cuba. Though the outward journey may be perilous, it’s the homeward trip where the real danger lies: U-boats prefer their victims deep-laden and full of cargo.

There have been heavy losses off Norway and Dunkirk – the vital priority is for escorting destroyers to counter the invasion threat. Odds are against any individual ship getting over 'the pond' and back.

Which will not do. Because Holt must get back to Britain in time to marry his girlfriend Julia, before the baby is born…