Yeah, the U-35 site is a real treasure trove of information http://www.psionguild.org/forums/ima...s/thumbsup.gif

You're quite right. I believe a few U-boat memoirs state that the Kriegsmarine and the U-bootwaffe in particular knew that the Americans were de facto conducting operations against them; the protection the Americans had extended only to their noncombatant units, namely merchant vessels and civilian craft flying the American flag. Warships accompanying the RN or conducting operations against U-boats were attacked whenever required or desired; the Americans lost several destroyers that were nominally sailing under the British flag but were crewed with Americans sailors and so on early on in the war, before Pearl Harbour.

However, because the US is supplying warships and the Lend-Lease Act is in effect doesn't mean that the US is providing bombers + crews and armoured divisions; so it was still in the German's best interest to fight it as they needed to and try to avoid drawing the Americans 100% into the conflict. There was still significant political opposition to American entry into WWII, partially due to residual Isolationism, partially due to the retarded conduct of numerous American generals during the latter stages of WWI (launching offensives on the last day of the war. Literally. There was a congressional hearing, a paper was published, and then promptly classified because the war had just ended and "America needed heroes", and the paper would have quite rightly tarnished a number of general's reputations) and Pearl Harbour erased that. So up until the Germans declaring war on America in support of their Japanese allies, they might have been able to avoid significant reinforcements in the form of combat troops to Britain.