He sets off and instinctively veers to the grass verge, which softens the tread of his boots. His thick black beard protects his face from the cold. With the dark navy fisherman’s coat over a thick knitted jumper he looks every inch the Norwegian fisherman indigenous to these parts. That he cannot speak a word of Norwegian does not bother Harry. The disguise is to make him look natural to any passing patrol.

Fifteen minutes later, he crests the top of the hill and starts the descent towards the dark harbour. No lights show for fear of the RAF. Blackness against a sea of blackness but the harbour is here, and in that harbour are U-boats and those U-boats are the target. Five of them reportedly brought in for service and repair. There will be guards, patrols, dogs, searchlights and rapid response units ready to mobilise instantly, but the element of surprise and sheer audacity might just see him through.

He drops down to one knee, letting his breath recover while picking out the darker silhouettes of the buildings and smiling at the first slivers and cracks of warm yellow lights showing in the windows and door frames. It’s no different to England or any other base he’s been on. Soldiers believe they are invincible and, despite the constant warnings, they cannot help but get lazy. Doors not quite closed properly, curtains not drawn tight enough. Soldiers need to drink and move about. Who would attack here anyway? Norway in the middle of winter? Against the army of the Third Reich? Not a chance. Anyway, an RAF pilot flying thousands of feet in the air cannot possibly see a tiny yellow light on the ground.

The next sentry post is manned properly with alert guards under the watchful eye of an officer. Harry stays low then drops on to his belly to snake over the freezing, stunted grass to the high-wire fence surrounding the town. In the shadows, he stops and pulls wire cutters from his pocket and sets to work. Each clunk is dull and seems to reverberate in every direction and he stops frequently to scan the vicinity and listen.

He works steadily, biting through the links before peeling back the fence and creating a hole big enough to squeeze through, but he backs away and belly-crawls along the fence to the sentry hut while keeping his head tucked low in the high collar to prevent the moonlight reflecting from the skin round his eyes, cheeks and nose.

Five metres out and he is close enough to hear the muted conversations of the guards and see the steam of their breaths. He pulls the explosive charge out, several sticks of dynamite wired to an electric timer. He turns the dial to set fifteen minutes and places it on the floor before belly-crawling back to the hole in the fence and through into the town.