Dank and dark, built by slave labourers, the vast concrete complex known as Valentin on the north German coast is not exactly a des res.

Germany's notorious submarine factory is, however, up for sale to anyone interested in a building with 7m-thick walls, the largest surviving bunker from the Third Reich.

The asking price is vague but government officials say that they could be accommodating for any serious bidder. The place has become a millstone, its upkeep swallowing up to €800,000 (£630,000) a year from the Defence Ministry budget. “And that's just the absolutely essential investments needed to stop the place crumbling,” says commandant Wolfgang zu Putlitz, who is in charge of guarding and maintaining the site.

Hitler, concerned that Germany was losing the edge in the war for the sea lanes, ordered the construction of the factory near Bremen with the aim of producing a new U-boat, the sophisticated XXI model, every 56 hours.

Germany had wreaked havoc on Allied shipping at the beginning of the war with a fleet of only 57 submarines. By June 1943 the tide was turning: the Allies had developed accurate detection devices that could outwit and trap the expanded U-boat force.

The factory, codenamed Valentin, was Hitler's last chance to stop the Allies ferrying supplies and reinforcements by sea. It was to be shielded from bombing raids by a bunker with a thick pre-stressed concrete roof.

The result was a silo with the dimensions of a cathedral: 426m (1,400ft) long, 97m wide, 25m high. At one end was a diving basin for the last tests on the U-boats before they would slide into the Weser river and head for the North Sea.

In the event, no submarine left the factory. By March 1945 the factory, begun 18 months earlier, was 80 per cent complete. Then a British Bomber Command raid succeeded in penetrating the roof. Barely a month later, before repairs were complete, the war was over.

The initial idea after the war was to blow up Valentin but that would have required at least 500 tonnes of explosives and the blast would have wiped out most of the neighbourhood. So it was taken over by the German Army, which has been using part of it as a storehouse. Blowing it up is now out of the question because it has been officially listed: research in Eastern European archives has shown that at least 4,000 slave labourers, many of them from Poland and Russia, died building Valentin. Most were undernourished. Some were beaten to death by guards trying to enforce a breakneck speed of construction.

“This bunker should not be sold,” the Mayor of Bremen, Jens Böhrnsen, says, “for both financial and moral reasons.” The new owner would have to commit himself to making at least part of the site into a memorial centre for Nazi slave labour. At least 12,000 concentration camp inmates, forced labourers and prisoners of war were involved in the almost pharaonic project: a million tonnes of gravel and sand had to be dug up and 1,232,000 tonnes of cement was mixed.

A British war crimes unit investigated conditions in the nearby work camp at Bremen-Farge and painted a horrific picture of life there: crammed sleeping quarters, back-breaking shifts, sadistic overseers, rations that would barely feed a child.

In 1947 12 German guards were charged in a Hamburg court with crimes against humanity committed at Valentin.

Franz Josef Jung, the German Defence Minister, has said that he is aware of the historical significance of the U-boat factory but added: “It is not the task of the German Army to maintain memorials”.

Grand designs

— The 325-acre Reichsportsfeld for the 1936 Berlin Olympics remains one of the most famous Third Reich projects. The stadium alone cost 42million Reichmarks and, though it could seat 110,000 people, it took only 13 and a half minutes to empty

— A retreat for Hitler in Obersalzberg became a complex of Nazi buildings with an “Eagle's Nest” almost 3,000ft higher than Obersalzbergmountain

— The Nazis planned five seaside resort complexes to provide workers with cheap holidays. Only one, at Prora, remains - the largest Third Reich building in existence

Sources: thirdreichruins.com; Times archives

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