The problem for the Germans was that Goering said the Luftwaffe would destroy the Allies at Dunkirk and that the German ground forces must wait for the air force to do its work. The problem for the Germans was that the bombs were much less effective on the soft beach sand. This gave the Expeditionary Force desperately needed time. Also the ferocious defense of the Expeditionary Force would have made the German ground forces happy to sit back and avoid extra casualties.