Fall Gelb, Case Yellow, was the codename for the German invasion of France and the Low Countries, carried out on May 10, 1940. German armored units punched through the Ardennes to cut off and surround the Allied units that had advanced into Belgium, outflanking the Maginot Line.
Fall Gelb had been devised by the famous General Erich von Manstein in collaboration with Heinz Guderian. The French had always thought that a German invasion through the Ardennes was almost impossible as it was a thickly forest-covered mountainous region with a bad roads. But Fall Gelb was a carefully thought out plan which relied heavily on the use of armor divisions, storm troops, and planes.
In Fall Gelb the German hit hard and quickly and France surrendered in less than a month. Much of the British army and large part of French and Polish army was able to escape in a series of evacuations called Operation Dynamo. The French Republic collapsed and was replaced by a "French State" headed by Marshal Henri Philippe Petain. His government based in Vichy became a loyal partner of the Axis for the rest of the war.
[...] battle took place from May 10 to June 14, 1940, and consisted of two main operations. In the first, Fall Gelb, German for "Case Yellow," German armored divisions made their way through the Ardennes [...]