Placing his right boot on a severed hull plate, Nash grabbed a broken steel beam and climbed inside. The experience was disconcerting, like being in a condemned apartment building that had frozen while toppling over. Nash tested every rusty handhold as he climbed. Many proved unsafe, and it was slow going. Resting on a horizontal door frame, he looked inside a small cabin scoured out by raging water. By the remains of a single bed frame, he guessed it had belonged to an officer.

‘God verdomp,’ Boerman growled behind him. ‘Hurry up.’

After fifteen metres and twelve empty cabins, the vertiginous corridor terminated in a bulkhead hatch which Nash didn’t like the look of. Assuming that it could be opened, it looked poised to slam down on their heads, and he looked back enquiringly at Boerman.

‘Get out of the way,’ he snapped impatiently.

Nash crouched on the wall of the adjacent cabin and watched the big man take a lump hammer from his belt. Like a blacksmith, he pounded the steel surface while Nash put his fingers in his ears to muffle the deafening clangs. The big man now grabbed on to the handle, swung his legs up and locked them into the sides of the passageway. Letting rip with a stream of unintelligible Afrikaans, he began to exert pressure. Hidden muscles on his arms popped out under the strain. With a shriek of protesting metal, the handle suddenly gave. With a grunt of satisfaction, Boerman began winding the door open.

Nash could hardly stand it. At any moment, he figured the heavy door would drop down and bat Boerman into well-deserved oblivion. But he was to be disappointed. As an internal hatch, it was hinged to swing away from the control room – so as to protect it in the event of an emergency – and Boerman needed all of his brute strength to shove it up and over.

Abruptly, the dank smell of a rarely visited basement washed over them.

‘Fucking unbelievable!’ Boerman exclaimed. ‘The water never got in here!’

They were stepping back in time. The cabins were exactly as they had been abandoned more than seven decades ago. Beds were still made, albeit dangling from the wall, their linen black with mould. Threadbare caps and uniforms hung askew from hooks. Mottled pictures of loved ones, bags and belongings lay scattered in corners. Traditional Japanese items evoked the land of the rising sun: tatami mats powdering in a pile; shattered saki bottles and tea sets; a katana samurai sword.

Nash felt like a grave robber disturbing a tomb. Boerman had no such qualms, and eagerly rifled through the artefacts. In the next cabin, they found a mouldy black uniform with death’s head badges, and a sleek machine pistol still shining under a thick layer of grease. Boerman picked it up and cocked the mechanism.

‘A fucking’ MP40 he breathed. ‘It’s in mint condition! I could pop you with it right now, Nash.’