[TteFAboB]

There were nine months of lend-lease before the official American entrance into the war, there was also the transfer of 50 DD's that could at least be used as cannon-fodder. I believe if the US was willing to let the Brits fall, Roosevelt would have kept his money and production to himself and wish the Brits good-luck, afterall, he could even make profits if he signed a deal with Hitler, for example, to sell aviation fuel or more bluntly Oil, while there was no money to gain with the lend-lease, not directly on the short-term, that is.

Another thing to consider, if Hitler had built 300 U-boats and even if the British didn't bothered to build anything to counter that believing in their superiority, it would still affect Hitler's resources and he would field less Panzers and Messerschmits. Would he still have enough to take down Poland and France? While the Polish campaign was a remarkable blitzkrieg, I have my doubts if a weaker German Army and Airforce would manage to win the French blitzkrieg, Hitler already had his "lucky" moments in the real campaign. A better opportunity of victory would happen if the Allies took the 300 U-boat threat seriously and cut funds from the Army and Airforce to invest in the Navy, then even a weaker German Army could've steamrolled through France, from then it would depend on how the British naval investments would pay off against the 300 U-boats.