At 6.50 AM, U-23 hits Danish oil tanker SS Danmark (anchored in Inganess Bay, Orkney Islands, Scotland) with one torpedo. Danmark breaks in two and drifts ashore; her crew of 40 escapes. She is carrying 14000 tons of fuel from Aruba in the Caribbean, depriving the Allies of valuable fuel supplies.
The capture of German invasion plans at Mechelen on Jan 10 has several consequences. France is alerted to the planned attack. French Supreme Commander Gamelin shrewdly uses the invasion scare to pressure neutral Belgium to allow access to Allied troops. Hitler learns of the breach and goes berserk, foaming at the mouth at Luftwaffe incompetence. He blames Luftflotte 2 commander General Hellmuth Felmy and replaces him with General Albert Kesselring. Captured Luftwaffe Majors Reinberger and Hoenmanns are sentenced to death in absentia. Hoenmanns wife dies under interrogation by the Gestapo.