Nazi Megastructures: U-Boat Base

(national Geographic, astro Ch 553, 11pm) It’s another episode showcasing the ruthless and admittedly exemplary (no matter how you feel about them) defence system of the nazis. To safeguard their u-boat submarines in port, immense and impregnable submarine pens were built to defy the force of the allied bombing raids. The sheer size and strength of these pens have earned them a place in history, as pure engineering achievements if nothing else.