I've just watched the WW2 From Space documentary and when the narrator was explaining how D-day went down the above question popped into my head.
Obviously the Germans were exceptionally strong since they waged war on multiple fronts. How come after several unsuccessful air invasions and bombings, they didn't decide to invade the Britain by land?
Shout if you have further questions but there's a thread from a while back, Why didn't Hitler do a D Day like landing to invade Britain?; /u/thefourthmaninaboat covers things thoroughly with links back to several previous posts on top of the comments there.