HMS Thunderbolt in action

15th December 1940: An Italian submarine is ambushed as it attempts to enter a French port with a German escort

The commander of a T class submarine at the periscope.

In December 1940, a number of Italian submarines were headed to the Gironde estuary in France, now the home of a Nazi U-boat base. What role intelligence played in compromising this move is not revealed in the contemporary reports, but a line of Royal Navy submarines was lying in wait.