Even with a rope, Nash took his time. With slippery surfaces and hard jagged edges, any kind of fall was potentially lethal. He was catching his breath, just above the topmost torpedo door, when Boerman’s big arm looped down.

‘You’re like a fucking old woman!’ he bellowed in frustration. ‘Take my hand!’

‘Thanks, but I’ll pass.’

A few minutes later, he reached the big man, crouched on the nose of the pneumatic catapult track. It was a precarious perch. Nash’s stomach contracted at another lethal drop to the circular waterproof hangar door.

‘Kom, we use it for a ladder.’

The garish smudge of rust across the left side of Boerman’s face made him look like an extra from a Mad Max movie. Unencumbered by rope or common sense, he climbed swiftly down through the remnants of the track mechanism, which had once flung five-tonne torpedo bombers into the air. The steel was treacherous. Sections which looked strong enough to support a car suddenly snapped in Nash’s hand.

‘What’s happening?’ Sura’s voice floated down.

‘Almost at the hangar!’ Boerman roared. ‘The door is closed!’

‘Be careful –’

There was a sharp snapping sound. In a shower of debris, the Afrikaner plunged several metres, landing feet first on the nose of the conical hangar door. Its steeply sloping sides offered no purchase, and Boerman’s boots slipped on the flaking rust. Slamming down hard on his side, he inexorably slid towards the edge, and Nash willed him to fall, but with a last desperate grab, Boerman managed to grasp a handle near the edge of the door and swung wildly to and fro like a pendulum.

Biceps bulging, the Afrikaner slowly hauled himself up. Nash inwardly cursed. Boerman was one of those people fate would simply not take care of.

‘Still here, Nash.’ Boerman grinned up at him. ‘I’m still fucking here!’

It took Nash ten minutes to negotiate the treacherous conical door on his backside, and his arms were shaking until he reached the secure handholds of a triple twenty-five mm anti-aircraft cannon mounted on the hangar roof.

A short distance below, Boerman was standing on the face of the offset conning tower.

‘Hopefully, we can get in this way,’ he said, before striding up to the top.

Something peculiar then struck Nash about his now-uninterrupted view to the stern. The entire deck was curved like a roller coaster track. He realised the submarine had bent like a giant banana from the tremendous force of crashing into the sinkhole floor, which must have cracked open the hull below.

He was heading over to Boerman when the rope abruptly pulled up taut. Nash realised he’d reached the end of the line.

‘Unclip your ass,’ jeered the big man. ‘Or I’ll come and get you myself.’