“Today the North Atlantic is as it hasn't been for months, alive with German submarines.”
“We are having ships sunk day by day.”
The only thing worse than January in the Battle of the Bulge is January in the Battle of the Atlantic.
Doenitz never fully bought into the invincibility of Enigma. I don't recall if this was one of the instances when he changed the naval Enigma codes but when he did, advantage swung back in favor of the U-boats until the allies could crack whatever had been done with the ciphers.