The Sunderland hurtled in like an avenging angel and two depth charges fell from beneath her wings. Seconds later two explosions signalled the end of the U-boat beneath her. Flight-Lieutenant Jack Gregory and his crew were jubilant, for the weary months of training and patrolling had paid off.

But they wouldn’t have been so happy had they known this was only the start of a long chase that would take them the length and breadth of a snow-covered Hebridean island…on foot!