" the planning, equipment and resources that went into D-Day just for the Neptune component."
but that was an attack on a fully equipped enemy which had had 4 years to prepare against invasion
In 1940 the British Army had lost almost all its heavy equipment in France and was totally disorganised - and the fixed defences were amateur. The RAF had fighters, which hadn't been adapted to carry bombs, but very little in the way of battlefield support. The Germans had a lot of kit and an airforce designed around battlefield support.