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It's a terrible idea, I'm sure of it, but hell, I'm gonna ask about it.
The wadden sea is a flatland that covers the entire German coast that's open to the North Sea. From there lies Bremen, Hamburg, and further in Hannover and such.
The AHC is to have the WAllies attempt and succeed in an amphibious invasion from the North Sea directly onto Germany, with the WI asking what the ramifications would be.
Here's a map of Germany.
Go wild.