Why did the Germans overestimate the US's ability to raise and supply an army?

As part of the invasion of Europe, the Allies did a TON of work to make the Germans think there was a massive amount of troops ready to invade that didn’t exist, right? And over this calendar year of coverage, it’s pretty clear that the US struggled to keep up with the need for supplies- such as landing craft.

And given that all of FUSAG’s supplies were made up- that’s both a huge amount of soldiers and supplies that just didn’t exist. But the Germans largely believed that they did- at least more than not.

Is there any evidence why the Germans thought the Americans could build and supply an army much bigger than the one they actually did?


The Germans were under no illusions about how much logistics and supplies the US could handle. They saw it first hand in Italy and to a lesser degree in North Africa so seeing a phantom army and fake logistics networks most likely made most of the German high command nervous.

Until Antwerp was liberated the main logistics and supply hub was still in the Dday areas where huge stockpiles of everything were stored from fuel to basic necessities to weapons and ammunition and the Germans knew about it but could do nothing about it. They no longer had air superiority and the V series rockets were very inaccurate.

The allies main weak point for logistics was the roads as so many civilians and military vehicles clogged the roads in France it was not uncommon for front line units to be down to their last box of ammunition. This is something the the Germans likely did not know and if they had known destroying road and rail networks would have caused nothing but headaches behind the front lines. As it was the civilian refugees and military columns did an admirable job of bogging down allied logistics and supply.


But what I’m more curious about is how they took the illusion of FUSAG hook, line, and sinker. So while they saw what the US could do, they also took it to a level that the US wasn’t capable of doing. And that extrapolation was a real issue relative to fooling them into thinking the main invasion was going to Pas Des Calais that included the diversion invasion at Normandy.

Sure, a lot of intel and fooling went into it, but someone should have done some calculations to see if the US could even raise and supply that entire army.