Signals warning and British fleet concentration

Germany's submarine force is estimated at 80-90 boats in total, with about 20-30 normally operating at a time. Concentrating more for Sea Lion would require withdrawals from the North Atlantic, and the movement of radio traffic could reveal that concentration through signals analysis. The designated anti-invasion force could also draw on available sloops, Hunt-class destroyers and Flower-class corvettes. A hypothetical discovery on the fourth day of a nine-day minelaying effort would leave Britain five days to assemble reinforcements. Ships might gather west or south of Ireland before entering the Channel at night. This area is considered less exposed to German submarines and reconnaissance while German submarine facilities in northern France were still developing. A missing British fleet could itself warn Germany to stop the attempt, so the scenario also depends on Germany choosing to proceed.