Army Group A was formed, through the redesignation of
Army Group South, on 26 October 1939 in the central sector of Germany's western frontiers, along the
France–Germany border and
Belgium–Germany border, in the broader area of the
Eifel and
Hunsrück mountain ranges. Under its previous name, the army group had fought in the
Invasion of Poland in September and October 1939. The initial commander and chief of staff of Army Group A were the same persons who held these portfolios during the time of Army Group South in Poland,
Gerd von Rundstedt as commander and
Erich von Manstein as chief of staff.
Preparations for the Battle of France Enthusiasm among the higher echelons of Army Group A for a repetition of the armored thrusts of the Poland Campaign was initially limited; Army Group A chief of staff
Georg von Sodenstern predicted as late as 5 March 1940 that a repetition of the swift advances through what was estimated to be a well-developed French defensive line was less than likely. Each of these armies as well as the panzer group were equipped with three army corps each, placing the army group at a total of twelve army corps. Additionally, Army Group A also received the concentration of German armored and motorized formations, as
5th and
7th Panzer Divisions (
XV Corps,
Hoth) were assigned to 4th Army and
1st,
2nd,
6th,
8th and
10th Panzer Division (divided among
XXXXI Corps (
Reinhardt) and XIX Corps (Guderian)) assigned to Panzer Group Kleist. Additionally, Panzer Group Kleist also received the
2nd,
13th and
29th Motorized Infantry Divisions (divided among XXXXI Corps and
XIV Corps (
von Wietersheim). Additionally, most of the 42 available reserve divisions were earmarked to support Army Group A rather than either of the other two army groups. and then swiftly turning northwestwards to rush towards the
English Channel and trap the Allied armies in the
Low Countries. 4th Army advanced on the army group's right flank (with
6th Army of Army Group B as its right-hand neighbor) from the
Monschau sector along the
Liège—
Namur axis as well as towards
Dinant. To its left, 12th Army stood in the army group's center, with its initial thrust directed from the
Prüm sector via northern
Luxembourg towards
Neufchâteau (Belgium) and then towards the Meuse river. Furthest in the south, the 16th Army held the army group's left flank and aimed to advance from the
Trier—
Merzig sector over
Luxembourg City towards
Longuyon. In its entire sector, Army Group A developed a large numerical advantage, advancing its own 45 divisions through territories held by only 18 enemy divisions. Within days of the beginning of the campaign, the troops of Army Group A achieved what one of the army group's staff officers, Günther Blumentritt, would later refer to as a "three-fold miracle": The Allied air forces failed to attack the lengthy tank columns that were stuck for hours on end in traffic jams trying to cross the Ardennes, the Germans succeeded with high speed and low casualties to cross the Meuse river with the breakthrough in the
Battle of Sedan, and the German tank divisions finally won a stunning victory in what was at times a more than reckless advance towards the channel coast, dangerously abandoning the cover of the German thrust's flank against a potential Allied counterattack that never materialized. There was a repeated tendency during the early days of the campaign where the Army Group A high command and the political leadership would advocate caution, but their instructions overruled and ignored by the divisional and corps commanders on the ground.
Georg-Hans Reinhardt of XXXXI Corps ignored a direct oder by the army group and instead advanced with his troops out of their bridgehead at
Monthermé. A similar action was undertaken by
Heinz Guderian of XIX Corps, who on 14 May was dissatisfied with the prospect of Army Group A leadership using his tanks to safeguard the bridgehead rather than to exploit the momentary disarray in the French army's rear. The leader of the panzer group, Ewald von Kleist, found himself in the difficult situation of mediating between his superior army group and his subordinate corps commanders; Kleist had initially covered Reinhardt's autonomous actions but was forced on 17 May to give a definitive holding order to Guderian, as Hitler personally had decreed a deceleration of the armored advance. This order remained in place until 19 May. When the operational delay of 17 May was revoked on 19 May, the tanks' thrust into the Allied rear continued. There was temporary panic among Army Group A higher-ups when on 21 May, a British attack hit the exposed German flank at
Arras, resulting in the
Battle of Arras. This attack was however repelled within hours. The first German forces had already reached the channel coast at 02:00 in the morning on 20 May, when 2nd Rifle Regiment of
2nd Panzer Division reached
Noyelles-sur-Mer. This left the northern sector of the French Army, the
Belgian Army and the
British Expeditionary Force cut off in the Low Countries. By 24 May, the Germans had encircled the critical channel ports of
Boulogne-sur-Mer and
Calais and were just 15 km off the last partially unobstructed port that the encircled Allied forces could use,
Dunkirk, where the Allies began to rapidly implement
an evacuation of their forces. Particular historical interest has been given to a sequence of events on 24 May 1940 known as the "halting order" (), where the armored formations were ordered to halt outside of Dunkirk and to instead prioritize infantry formations in the
Battle of Dunkirk. Popular imagination of both German and Western Allied postwar observers was captured by the idea that the German tanks might have inflicted horrific casualties on the encircled and tightly packed Allied infantry, if they had not been stopped by undue meddling by higher military command. Hitler had personally insisted on the preservation of the remaining tank forces on 24 May, overruling even
Walther von Brauchitsch, the commander-in-chief of the German army, after a worrying 23 May report by Ewald von Kleist had placed the casualties of his panzer group at "over 50%". Hitler in this concurred with the leadership of Army Group A and went against the intuition of von Brauchitsch, who even attempted to transfer the 4th Army away from Army Group A to insist on his own vision. Due to a coincidence, Hitler happened to be present at Army Group A headquarters on 24 May, and overruled Brauchitsch's instructions, implementing instead the "halting order". The halting order was revoked on 26 May and Dunkirk captured on 4 June. While the British army had been forced to leave behind much of its heavy equipment (including 475 tanks), some 340,000 British and Allied soldiers were successfully evacuated out of Dunkirk. After the Allied evacuation at Dunkirk, Army Group A tuned southeast and advanced in the general direction of the
Vosges mountains and the
France–Switzerland border, thus encircling the static French forces positioned along the
Maginot Line.
Occupation of France On 10 October 1940, Army Group A became the first army group upon whose commander the designation of
Supreme Commander in the West was bestowed, thus placing them in charge of the military dimension of the
German occupation of France. On 15 April 1941, this responsibility was passed to
Army Group D. Army Group A had in the meantime been repurposed on 1 April 1941 and earmarked for deployment to
German-occupied Poland.
Preparations for Barbarossa Starting on 1 April 1941, Army Group A was assigned the cover name Section Staff Winter (), later changed to Section Staff Silesia (), to prepare for
Operation Barbarossa, the
German invasion of the Soviet Union. On the day that this offensive began, 22 June 1941, Army Group A was formally renamed "
Army Group South", thus ending the first deployment of Army Group A. == Second deployment, 1942–44 ==