U-Boat Bases and Bunkers: U-Boat Bunker roofs were passively protected with Fangrost bomb traps which consisted of concrete beams with curved upper surfaces laid at perpendicular angles to each other creating a grid over the entire roof. Any bombs that hit the roof would detonate against the beams and the blast would be dissipated amongst the spaces between the beams rather than downward into the roof.
Charles McCain is a Washington DC based freelance journalist and novelist. He is the author of "An Honorable German," a World War Two naval epic. You can read more of his work on his website: http://charlesmccain.com/ View all posts by Charles McCain