Documentary: Nazi Mega Weapons: U-boat Hangar

One of the largest construction projects ever undertaken was the building of the submarine hangar in France at the sea port of --.  This in truth was three projects, each more astounding than the one before.  At first the Nazis used existing equipment to dry dock he submarines.  This was effective in get the submarines out of the water for repair, but left them vulnerable to air attach as there was no protection.  The Nazis constructed two large hangars where the boats could be stored.  These were made of thick concrete.  They also had rounded roofs so bombs would bounce off.  However these large hangars were yet too small to accommodate the larger U-boats.  A large project was undertaken.  Hangars K-1 and K-2 were build.  The foundation. Was too soft, even with driving steal beams into the earth for a foundation.  This limited the weight and the strength of he protecting ceiling.  These two hangars required transfer from one to the other with a delicate mechanism, and vulnerability to Allied aircraft.  An even larger bunker was needed.  This time the dug to bedrock for an even stronger foundation.  The roof was essentially nine feet twice, with a layer of air between two thick concret roofs.  A special bunker buster bomb call a "tall boy" was used.  This bomb destroyed the first roof where it hit, but did nothing to the second layer.  Since the hangar could not be destroyed, the Allies bombed the town.  They destroyed the town, but not the hangar and the submarines where still protected when in port.  Finally the plan shifted to killing the submarines at sea.  With better technology, and cracking the enigma code, the Allies were able to destroy the U-boats at sea.  They attacked them with planes, destroyers and destroyer escorts.  The hangar was impenetrable, and did not surrender until two days after the surrender of Germany.  However the Allies did win the battle for the Atlantic.