You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser.
alternatehistory.com
IOTL in January 1942 Hitler was convinced that the Allies were going to invade Norway so he locked down 20 Uboats in the area denying them to Doenitz for other operations, especially the extremely successful Paukenschlag on the US East Coast that resulted in over 600 ships sunk for over 3 million tons of shipping from January through August https://en.wikipedia.org/wiki/Second_Happy_Time
Initially of the 20 Type IX Uboats with the range to reach and stay on patrol in the area only 5 were available. What if all the Uboats used to guard Norway were instead used against the US? The Type VIIs showed up with the 'milk cow' variants to help supply and keep them on station later, but they had some issues with supply loads available. Nevertheless they were valuable on station.
So what if an additional 20 Uboats had been available for operations against the US from January 1942 on? Would that prompt the US to convoy earlier or would the slaughter continue until the US had enough escorts available? Is it conceivable that the Uboats could have sunk double the numbers of OTL?