To create a haven in port for their lethal U-boat submarines, the Nazis built massive, impenetrable concrete submarine pens. Structures too immense to be hidden, they were constructed to withstand direct hits from even the biggest Allied bombs. Such was their size and strength that these pens survive today, a testament to their engineering.
"U-Boat Base" on Nazi Mega Weapons airs on Wednesday, December 10th at 9 pm on channels 3 and 3-1.