Following French backtracking on mining the River Rhine (due to their fear of German reprisal bombings), British Prime Minister Neville Chamberlain calls off mining the Norwegian coast planned for April 5. Chamberlain tells the French ambassador in London Charles Corbin “No mines, no Narvik!” This act of bravado leads to a delay which will prove to be costly.
German armed merchant cruisers (Hilfskreuzer) Atlantis, Orion and Widder depart from Kiel, with WWI battleship SMS Hessen acting as an icebreaker, for operations against Allied shipping. Atlantis will prove the most successful German commerce raider, sailing 100,000 miles and sinking 22 ships (over 140,000 tons) in a voyage lasting 602 days (until November 22, 1941). http://www.bismarck-class.dk/hilfskreuzer/atlantis.html
Oberleutnant zur See Hans-Wilhelm Behrens falls overboard from U-43 and drowns in the Atlantic.