Adolf Hitler intended to attack in the west shortly after the annihilation of Poland. It took a great deal of persuasion to defer the action. First the re-deployment of the Army, the bulk of which was in Poland would take time. Second, the so-called "Light " divisions had proved far from satisfactory, and converting them to Panzer divisions via re-equipment and re-organization would also take time. then there was the shortage of artillery rounds and air ordinance that had to be replaced. So the start date was rolled back later and later in to the Fall. And then when winter set in, the attack was postponed until the Spring.
NEW PLAN, SAME AS THE OLD PLAN:
The initial plan for the attack in the West [Case Yellow] was a very minor variant of the Schlieffen Plan that the Germans had undertaken in 1914 [with Private Hitler in attendance]. The German Army was organized in three Army Groups, from north to south, Army Group B [Gen. Fedor von Bock], facing Holland and Belgium; Army Group A [Gen. Karl Gerd von Rundstedt], facing France from the left of Army Group B to the edge of the Maginot Line, and Army Group C [Gen. Wilhelm Ritter von Leeb], facing the Maginot Line and the border of France down to Switzerland.
The plan was for Army Group B, with the bulk of German armor, to thrust through Belgium [as in WW I], and Holland [newly added], and wheel to the southwest toward Paris. Army Groups A and C were basically to remain on defense, with local attacks to pin down the French.
When Hitler was first briefed on the plan, in the autumn of 1939, he was less than enthusiastic. At one point during a briefing by Gen. Alfred Jodl, Chief Operations officer of OKW [Oberkommando der Wehrmacht], Hitler pointed to the Belgian Ardennes, a heavily forested area just north of the French border, in Luxemburg and Belgium, and asked about the area's potential for attacking. Since most militaries [including the Germans] thought the area was not suitable for armor, Hitler was led back to the plan as it was.
Then during that winter, a German Courier aircraft landed, in heavy fog, in Belgium. A copy of the plan for Case Yellow was captured by the Belgians, and shared with the French and British militaries. This led to two things. The Allies modified their own plans, and pulled their only reserve army [ the Seventh]to the left of their line, so that when the Germans attacked they could move forward to the Dyle River line, covering southern Belgium and the southern tip of Holland. That reserve army had been located behind Sedan.
The second thing that happened was that the Germans paused to re-think and re-cast their plans. Enter General Erich von Manstein [formerly von Manstein und Lewinsky], the Chief of Staff of Army Group A. Manstein had never been happy with the original Case Yellow. He considered it pedestrian, probably anticipated by the Allies, and fundamentally flawed, because the bulk of the Panzer Divisions would be attacking on ground crisscrossed with a large number of water obstacles, and probably, large numbers of Allied troops [the Allies outnumbered the Germans in the number of troops, and tanks].
THE SICKELSCHNITT the Scythe Cut]
Like Hitler the autumn before, Manstein looked at the Belgian Ardennes. Unlike Hitler, however, he consulted Germany's leading Panzer expert, Gen. Heinz Guderian, about the feasibility of moving large bodies of armor through the area. When Guderian opined that it could be done, Manstein recast the entire operation in the West. Army Group B was reduced to having only three Panzer Divisions [one for Holland, two in Belgium north of the Ardennes]. Army Group A was now assigned seven Panzer Divisions to attack on a front of roughly sixty miles, from the vicinity of Dinant to Sedan. Those divisions [and their supporting Infantry Divisions] were to attack through the Ardennes, cross the Meuse, and drive to the Channel, cutting the Allied line in two, and encircling the Allied forces in Belgium. was to act as the cape, luring in, and pinning down the Allies, while Rundstedt ran around the Allies' right flank. Leeb was to conduct attacks on the Maginot line from the front, to keep French forces there from attacking or deploying elsewhere.
In addition, the Germans planned some complementary operations in Holland and Belgium to facilitate the offensive. First, German airborne troops were dropped in Holland to seize bridge. Second, Luftwaffe attacks were made on most of the Allied airfields near the front. Third, in a plan apparently conceived by Hitler himself, glider borne Luftwaffe paratrooper combat engineers were landed on the Belgian fortress of Eben Emael, the key defensive position of the Albert Canal line. Eighty men, using shaped charges, captured the fortress, and over a thousand prisoners, and tore open Belgium's defensive position.
THE EXECUTION
The attack began on May 10th. While all eyes were focused on Holland and Belgium, where the Allies moved forward to the Dyle line, seven Panzer Divisions moved through the Ardennes, all arriving at the Meuse River by May 13th. By the end of the 13th, Guderian's XIX Panzer Corps had something like an eight mile bridgehead at Sedan. At Dinant, the 7th Panzer Division, under its new commanding general, one Erwin Rommel, had crossed during the night and was racing west. With no major reserves in front of them, the Germans stormed to the coast. Three counterattacks, two by the French [Col. Charles DeGaulle], and one by the British [at Arras] were beaten back, although the latter panicked the German High command, leading to an ill advised, albeit temporary halt. When the Germans resumed their attacks, they began snapping up the Channel ports. But the delay cost them one, Dunkirk, and the British Expeditionary Force [minus their artillery, vehicles and heavy equipment] and a fairly large number of French troops escaped Belgium and Holland had already surrendered]. By the beginning of June, the Germans turned south to finish France.
EVALUATION
This is, of course, my opinion only. Having said that, I would rate Case Yellow as the greatest military operation of modern times, and second only to the Mongol invasion of eastern Europe in 141-1242 on the all time list. It was a brilliant combination of divining enemy intent, and using that intent as an integral part of the plan. It took full advantage of the combat experience and effectiveness of the German troops, vis a viz their opponents, as well as the superiority of German doctrine and equipment, particularly the close support capability of the Luftwaffe. It drove the British out of mainland Europe, and led to a French surrender six weeks after it commenced.
