4. German Invasion of Denmark
Updated: May 27, 2018
Although Strategically unimportant, Denmark had an airfield at Aalborg that would allow the Luftwaffe to operate over Norway. The Danes trusted a non-aggression pact they had signed with the Germans, and did little to mobilize or prepare defences.
The Germans invaded on April 9, 1940, and overran the entire country in less than 40 hours.
Here is the link for the scenario if you want to play it for yourself!