Why air success alone would not make Sea Lion viable

Winning an air campaign would not itself give Germany control of the Channel. Royal Navy capital ships, cruisers, destroyers, motor torpedo boats, submarines, and radar-equipped forces could move at night when Luftwaffe anti-shipping power was far less effective. A U-boat barrier could inflict losses, but 1940 Germany lacked the later-war submarine numbers and surfaced boats redeploying against radar-directed cruisers would be vulnerable. British carrier aircraft and whatever land-based fighters remained could concentrate over the fleet while it attacked the crossing, making Sea Lion a naval problem that air superiority alone could not solve.