Specialist E-boat crews could slip inside coastal convoys by approaching without the obvious movement of an attacking craft. On early radar, a contact moving only with the current could resemble wreckage, a buoy, or another harmless object. Relative motion was an important part of deciding whether a faint return represented a threat. Radar detection alone did not solve the harder problem of identification within crowded waters.
Notable Point · 10:27-12:04
Why early radar could mistake an E-boat for debris
Early radar could struggle to distinguish a stationary or slow E-boat from wreckage or a buoy, creating an opportunity to drift among convoy traffic.