A period of the Second World War between October 1939 (i.e., German Case White, the invasion and the fall of Poland) and April 1940 (i.e., Weser Exercise or WESERÜBUNG NORD) the invasion of Norway), was called the Phony War, or, in a pun on blitzkrieg, sitzkreig. There was relatively little U.K. combat during this period. While there was a good deal of intelligence work, very little was done to redeploy troops.
The major operations following were Case Yellow/Fall Gelb, the invasion of France and the low countries, followed by the Battle of Britain and the German planning for the invasion of Britain, Operation Sea Lion.
Gernany's Oberkommando der Marine ordered several major operations and some lesser commerce raiding, as they built up the submarine arm. The two major operations were the Battle of the River Plate, after which the German "pocket battleship" DKM Graf Spee was scuttled, and the raid on the British naval base at Scapa Flow in Scotland, in which the German submarine U-47 sank the battleship Royal Oak.
Going into the Norway decisions were a variety of factors. 
- Kennedy, Robert M. (April 1956), The German Campaign In Poland (1939), U.S. Department of the Army, DA Pam No. 20-255
- Lindemann, Timothy F. (March 1997), Joint Operations Case Study, Weserübung Nord: Germany's Invasion of Norway, 1940, U.S. Air War College, U.S. Air Force, AU/ACSC/0146A/97-03
- Ziemke, Earl F., Chapter 2: The German Decision To Invade Norway and Denmark, Command Decisions, Office of the Chief of Military History, U.S. Army