Operation SEALION examines just how realistic the German threat of invasion was. The author studies the plans, the available capability and resources, the Germans' record in Norway and later Crete. The author weighs these against the state of Britain's defenses and the relative strengths of the land, air and particularly naval forces.

The unstoppable hun -- After Dunkirk -- Lessons of invasions past -- The Germans prepare their plans -- The Battle of Britain -- The state of the navies in 1940 -- Woe to the conquered-German occupation in the East -- Woe to the conquered-German occupation in the West -- The lessons of Crete -- Babbarossa and Deliverance -- What would have German occupation meant? -- The lessons of Normandy -- Could the Germans have invaded?.