How would a completed Channel Tunnel affect the Allied retreat from France in 1940?
Short answerIt could evacuate troops and equipment efficiently, then would probably be flooded to prevent a German invasion route.
NotesThe tunnel would let the Allied perimeter contract while trains loaded out of direct observation deeper underground. It could move far more heavy equipment than an improvised beach evacuation and reduce dependence on small craft. German air attack would make the terminals and approaches dangerous, but the protected rail route would still be valuable while open. Once the retreat ended, British defenders would likely destroy or flood the link and rebuild it only after the war.