Since you have recently had the experience of playing the Western Allies ...can Germany win the race and make the Allies start over by kicking them off the continent?
Interesting question, and probably not surprisingly, I have thoughts on the matter.
Truth to tell, I think against a careful German, a Western Allied D-Day invasion is a tricky problem. I have seen the Allies over and over again blow a D-Day invasion because of inadequate preparation. When a D-Day has worked, it is often because of inadequate response on the part of the Germans or because they were already too far down in the game and the invasion was just a coup de grace anyway.
Assuming good European Axis play, my rule of thumb is that the Western Allies need something like 15 to 18 transports available before making any serious attempt to go ashore in say 1943 or 1944. About eight transports are needed for shuttling builds from the US while the rest are needed for the invasion and subsequent build-up.
The Allies also MUST have something like at least twice as many troops within two sea zones of the beachhead as they can max carry in the invasion transports. In other words, 15 to 20 transports worth of troops need to be in 'inventory' (say two-dozen infantry and 20 tanks) and this needs to be above and beyond what is landed in the first wave. Less than these quantities (let alone much less) and I think the Germans can often get a pretty good chance of smashing the invasion (and which would rate to set the Allies back a good year).
The Allies also almost certainly need air dominance if not in fact air superiority (those transports are just too vulnerable otherwise). I wonder if Mark still remembers the time I had 19 German fighters to his 11 Allied, chasing off his transports and thereby isolating the beachhead from further reinforcement...
If the Allies don't have the requisite depth of troops ready-to-hand near the beachhead they tend to run out of troops the third or fourth turn of build-up (and which is the usual mistake they seem to make when a game gets this far). At that point, they have to start strategic moving transports back and forth between US/Britain and the beachhead, with transports now only delivering troops every other turn instead of every turn and with some of them actually going empty for lack of troops. The consequent loss of build-up tempo can give the Germans dominance over the build-up.
The Germans need to rail in a large fraction of armor and artillery to do this right, and which should be a no-brainer if they can see the Allies have inadequate depth. When the timing is right, they strategic back every Axis plane in Europe to neutralize Allied air power and then quite possibly you can scratch one beachhead (and which probably has no retreat options...). Of course such a German reaction does take tremendous pressure off the Eastern Front and for which Uncle Joe Stalin will no doubt be grudgingly appreciative. Meanwhile though, the Allies have just lost a pile of irreplaceable troops.
I really like this aspect of the game (a Western D-Day). It often does not come up, but when it does, the game indeed seems to reproduce the Allied historical problem of having sufficient landing craft and the difficulty of winning the battle of the build-up.
Oh, and one last thing: Guess why as the US player I always max on tank production starting right at Pearl Harbor? I suspect that the pile of tanks might be the only thing capable of standing between massed panzers and an annihilated beachhead.
dd