Good post. I like the analogy to WWI. The United States was already giving critical support to the Allies, the Germans thought active belligerence wouldn't make their situation significantly worse, and they considered the prospect of winning the war by unrestricted submarine warfare was worth the risk. The ability to operate U-boats freely throughout the Atlantic is the only benefit I can think of that the Germans derived from declaring war. I agree it's hard to imagine the US staying out of the war, but I've posed the question many times, without any real response, when FDR could have asked Congress and the American people for a declaration of war or what arguments he could have used to make his case. He didn't say a word about it on December 8, which would have been the perfect time to point out - perfectly correctly - that Germany and Japan were allies and that Japan's action was facilitated by Hitler taking on the British Empire, France, the Netherlands, and Russia. Although most Americans had come to accept that we might get dragged into the European war, there was little support for us taking the step - especially when we suddenly had a real war in the Pacific. Even if we assume that the US would be in the war at some point, there was no value to Hitler in declaring war on Dec 11. AFAIK the Germans had no specific knowledge of their "ally"'s plans. It took over a month to get just five U-boats deployed to American waters. The U-boats did enjoy a few months' "Happy Time", but that was transitory. Historically, after Pearl Harbor the US Navy started transferring warships to the Pacific (including some which had been brought east a few months earlier to enforce our "neutrality" zone), but the number of destroyers in the Atlantic Fleet remained stable*. If we were not at war with Germany, more of our newest DDs might have been sent to the Pacific. * Good discussion of this in Clay Blair, Hitler's U-boat War.