One of the core strengths of the German Army was its leadership
to men ratio. It was significantly higher compared to the allies. I
can't remember it off hand, but i'm sure something will turn up
quickly through a web crawl.
I'm not saying that we are "Fortress Singapore." Just that an
invasion force will have too much to contend with. The first front
being the Intelligence Battle. Its very HARD to hide a major force
build up.
Another of Hitler's mistake was overconfidence in the
"blitzkrieg."
1. The blitzkrieg is over rated. It was an excellent tactic when
numerically superior, technologically superior, as it prevented the
enemy from massing enough firepower to slow the advancing armor.
Airpower is a MUST. Against a technologically equivalent allied
army, with lesser tanks than the allies, the Blitzkrieg failed
him.
2. Hitler's personal meddling in Tank design, that resulted in the
monstrosity called the KingTiger and its predecessor, the Tiger,
added the final nail into the blitzkrieg coffin. The hideously slow
and ultra heavy tank could not keep up with blitzkrieg style tempo
of ops. Firstly, its a gas sucker, and too heavy for the terrain
they were supposed to operate in.
3. Hitler's lack of confidence in his commanders, and the German
Army's capability to fight defensive battles. The German's were
experts at defensive operations. They were extremely organised and
more than capable of slowing and inflicting casualties on a
defensive fight. He failed to allow his commanders to conduct
defensive battles in depth, instead ordering them to counter-attack
(blitzkrieg style, yes) whenever the opportunity arose. Fear of the
secret police saw to it that the commanders obeyed that
order.
Finally, I believed if Hitler allowed Rommel to position armor
behind normandy, the allies could not have gotten a beach head at
all. They would have been counter attacked immediately on the
beach. Instead, armor was positioned more centrally, in a more
conservative bet that they would be able to counter-attack against
any location the Allies chose to land. He should have gambled with
the DesertFox.