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 engines that could not reverse and drowned out spoken orders. It covers swimming tanks with kapok-filled pontoons, deep-wading tank crews told to sit underwater for up to six hours until the tide went out, four planned minefields, a decoy fleet of disguised ocean liners, cables dropped on power lines to black out southeast England, and the 1974 Sandhurst war game that concluded the invasion force would have been cut off and forced to surrender within six days.

• Why crane-transferring tanks at sea could take 14 hours per wave and required a dead calm
• Directive No. 16 and Hitler’s hope for a negotiated peace before ordering an invasion
• The Black Book listing 2,800 Britons for arrest and the plans of Franz Six for occupied London
• Proposals to move Nelson’s Column to Berlin and a pre-printed English edition of Mein Kampf
• How the postponement on September 17, 1940, turned Hitler’s attention toward the Soviet Union