This was the period of Operation Paukenschlag, the German U-boat campaign that began hitting every ship on the Eastern Seaboard - ships that were skylined by the lights of the cities at night and were easy targets for them
The U-boat commanders spoke of this as "the happy time", where the Allies didn't have their act together yet for anti-sub warfare. That changed in the course of a year...
I thought FDR covered it up for more than a year.