The 4th Army was activated on 1 August 1939 with General
Günther von Kluge in command. It took part in the
Invasion of Poland of September 1939 as part of
Army Group North, which was under Field Marshal
Fedor von Bock. The 4th Army contained the
II Corps and
III Corps, each with two infantry divisions, the
XIX Corps with two motorized and one panzer divisions, and three other divisions, including two in reserve. Its objective was to capture the
Polish Corridor, thus linking mainland Germany with
East Prussia. During the attack on the
Low Countries and France, the 4th Army, as part of Field Marshal
Gerd von Rundstedt's
Army Group A, invaded Belgium from the
Rhineland. Along with other German armies, the 4th Army penetrated the
Dyle Line and completed the trapping of the
Allied forces in France. During the Western Campaign, the 4th Army was at the center of an organizational dispute between Army Group A,
Army Group B, the Army High Command (
OKH) and
Adolf Hitler. The commander-in-chief of the army,
Walther von Brauchitsch, was dissatisfied with the size and leadership style of Army Group A, especially its commander Rundstedt; on May 23, 1940, the OKH ordered that the 4th Army should be subordinated to Army Group B from 20:00 on the following day. As a result of this order, Rundstedt would have lost all the armored units (
Panzer Group Kleist,
Panzer Group Guderian) of his army group. According to the OKH's concept, Army Group B was subsequently to be utilized for the reduction of the Dunkirk sector of the front and Army Group A merely for flank security. When Hitler arrived at the headquarters of Army Group A near Charleville on the morning of May 24 and learned of the OKH's order, he immediately suspended it. The 4th Army remained with Army Group A, followed at 12:45 by the famous
halting order, according to which the attack on the encircled Allied troops at Dunkirk was to be delayed until the infantry units (
II Corps,
VIII Corps) had caught up. The then Major-General
Erwin Rommel, who was under Kluge, contributed immensely to the victory of 4th Army. Kluge, who had been
General of the Artillery, was promoted to Field Marshal along with many others on 19 July 1940. ==Operation Barbarossa==