| 1939 | |
| 1 September | Germany invades Poland, starting World War II in Europe. |
| 3 September | Britain and France declare war on Germany. |
| 10 September | The British Expeditionary Force (BEF) begins arriving in France. |
| 27 September | OKW initial planning conference for the assault on the West. |
| 9 October | Hitler’s ‘War Directive No. 6’ orders the OKH to begin planning for the invasion of northern France and the Low Countries. |
| 19/29 October | OKH produces the original/revised Fall Gelb plan for the Western offensive. |
| 24 October | Heeresgruppe A headquarters established at Koblenz. |
| 31 October | First Heeresgruppe A memorandum to OKH urging a complete change in the concept of operations of the Fall Gelb plan – it is rejected. |
| 20 November | Hitler’s ‘War Directive No. 8’ orders the OKH planning to be flexible enough to shift the Schwerpunkt of Fall Gelb from Heeresgruppe B to Heeresgruppe A if an opportunity for greater success in the south presents itself. |
| 1940 | |
| 10 January | German courier aircraft mistakenly lands near Mechelen, Belgium, and copies of the airborne portion of the Fall Gelb plan are captured. |
| 25 January | Fall Gelb plan is revised to include the occupation of Holland. |
| 7, 14 February | Heeresgruppe A ‘war games’ convince OKH Chief of Staff, General Halder, that a major revision of the Fall Gelb plan is necessary. |
| 17 February | At a luncheon Hitler hears Manstein’s recommendation to shift the Schwerpunkt of Fall Gelb to Heeresgruppe A. |
| 18 February | Halder delivers to Hitler a completely rewritten draft OKH plan, which places the Schwerpunkt of the attack through the Ardennes – Hitler orders the Fall Gelb directive to be changed accordingly. |
| 24 February | Hitler signs the Aufmarschanweisung Nr 4 Fall Gelb deployment order. |
| 20 March | Général Gamelin, Supreme Commander of Allied Armies, adopts ‘Dyle–Breda’ designed to meet the German invasion in Belgium while the Maginot Line holds the French frontier. |
| 9 April | German naval units, army divisions, and Luftwaffe squadrons begin the invasion of Denmark and Norway. |
| 10 May | Fall Gelb – German invasion of the West – begins. |
| 12–13 May | The battle of Gembloux, focusing Allied attention in the north while German Panzers approach through the Ardennes in the south. |
| 12–14 May | The battle of Dinant – Rommel crosses the Meuse against a disorganized defence. |
| 13–14 May | The battle of Sedan – Guderian overwhelms unprepared French defences – Huntziger withdraws southward; Guderian turns west. |
| 14–15 May | Reinhardt crosses the Meuse at Monthermé and drives to Montcornet; the breakout begins. |
| 16 May | Rundstedt’s first ‘halt order’ is issued and either ignored or not received by Panzer units. |
| 17, 19 May | De Gaulle’s counter-attacks have no effect on the German advances. |
| 18 May | Following a crisis in command, Guderian is allowed to continue a ‘reconnaissance in force’. |
| 19 May | Gamelin is replaced by Général Weygand – Panzers released to continue advance. |
| 20 May | Panzers reach the English Channel, cutting off all Allied forces north of the Somme River. |
| 21 May | BEF spoiling attack at Arras stuns German Army leaders. |
| 22 May | Panzers invest Calais and Boulogne. |
| 23 May | Lord Gort orders the BEF to withdraw to Dunkirk. |
| 24 May | Rundstedt again orders the Panzers to halt – Hitler affirms decision with the OKW-directed Haltbefehl. |
| 26 May | Operation Dynamo – evacuation of BEF from France – begins; Hitler rescinds the Haltbefehl. |
| 28 May | Belgian Army surrenders. |
| 31 May | French 1ère Armée surrenders at Lille. |
| 4 June | Evacuation of Allied forces from Dunkirk ends. |
| 5 June | Fall Rot – final conquest of France – begins. |
| 22 June | France signs armistice with Germany. |