British naval preparations included the concentration of nearly 60 destroyers at certain points. Britain also understood that the proposed landing required high tides. One explanation is that reconnaissance of large numbers of flat-bottomed transport craft revealed the likely operating method. Another is that penetration of German intelligence and communications had already supplied the plan. A combination is considered plausible, with separate intelligence channels meeting higher up the command chain to corroborate the warning.
Notable Point · 38:07-39:36
How Britain could anticipate the tidal window
The assembled barges could reveal tidal constraints, while reconnaissance and intelligence penetration offer possible explanations for British knowledge.