The invasion of Denmark and Norway is set for April 9. Hitler allocates 6 divisions (including specialist mountain infantry and paratroops) 20 light tanks and 3 experimental Neubaufahrzeug heavy tanks for Norway, plus 2 divisions for Denmark. Almost every available naval vessel will be used to transport or protect these troops. Luftwaffe will provide air support and chase off Royal Navy ships trying to intercede. This is in contrast to the small, mainly reserve, force the British intend to send to Norway without air cover.
Almost alone among the senior British military, Vice-Admiral Max Horton (commanding Royal Navy home-based submarines) anticipates a German invasion of Norway. He orders 12 submarines (including 2 French and 1 Polish vessels) to patrol the southern North Sea and the seas around Denmark, to intercept warships from naval bases German coast. HMS Sealion is the first to leave, departing Harwich naval base for the Kattegat, East of Denmark.