Picture a 20-ton tank driving blind along the floor of the English Channel, sealed with caulk and waterproof tape and breathing through an 18-meter rubber hose. That was a real engineering solution for Operation Sea Lion, Nazi Germany's 1940 plan to invade Britain. This episode explores why the German military was reduced to such measures: a Kriegsmarine gutted by the Norwegian campaign facing a vastly larger Royal Navy, an army that treated the Channel like a wide river, and a compromise that narrowed the landing front to Sussex and Kent without producing a single purpose-built landing craft.

The episode examines the improvised armada of about 2,400 flat-bottomed inland river barges requisitioned from across occupied Europe, most of them unpowered and towed in pairs by tugboats, along with barges pushed by surplus 600-horsepower aircraft e ...