The I Army Corps () was a corps of the German army during World War II. It was active between 1934 and 1945, and participated in the Invasion of Poland, the Battle of France and the campaigns on the Eastern Front before eventually ending the war trapped in the Courland Pocket.
Operational history
Peacetime
The I Army Corps General Command () was formed in October 1934 from the 1st Division of the Reichswehr. Like the 1st Division before it, the I Army Corps was headquarted at Königsberg in East Prussia. The final commander of the 1st Division, Walther von Brauchitsch, became the first commanding general of I Army Corps on 21 June 1935.
Invasion of Poland
I Army Corps participated in the Invasion of Poland as part of 3rd Army (operating from East Prussia) of Army Group North, Its subordinate divisions were Panzer Division Kempf (with SS Regiment Großdeutschland and 10th Panzer Regiment), 11th Infantry Division and 61st Infantry Division. Walter Petzel was the corps commander of I Army Corps. 3rd Army operated in two primary directions of attack; whereas XXI Army Corps was to attack in a southwesterly direction against the Polish Pomeranian Army in the Polish Corridor in order to support the attack of 4th Army from the Hinterpommern region into the Corridor, I Army Corps and Wodrig Corps (later redesignated "XXVI Army Corps") instead were aimed southwards against the Polish Modlin Army, which was headquartered at Modlin Fortress and whose forces defended the northern border to East Prussia in strongpoints such as Mława and Różan.
In the morning of 1 September, I Army Corps stood ready in its starting position south of Neidenburg (), with Wodrig Corps in close proximity, southwest of Willenberg (). The two corps crossed the border towards the forces of Modlin Army at Mława, about whose defenses (including anti-tank fortifications) the Germans had gathered intelligence from agents since at least 21 August. In this sector, the Battle of Mława would be fought for the three opening days of the campaign. With 11th Infantry Division in the vanguard, units of I Army Corps crossed the border around 05:00 and met forward resistance from the 7th Company of the Polish 80th Infantry Regiment, which forced a delay on German operations. This time was sufficient for the 20th Infantry Division to collect and organize its forces, scattered as garrisons throughout local villages. As units of the 11th Infantry Division reached the Polish main line of defense, four kilometers north of Mława, they were met with defensive fire from the Polish 78th Infantry Regiment. As Panzer Division Kempf led an assault down the Neidenburg–Mława road with two Kampfgruppen formed from the personnel of SS Regiment Großdeutschland (in what became the first combat engagement of the Waffen-SS in World War II), but met concentrated fire from the Polish 20th Light Artillery Regiment at Uniszki Zawadzkie and had to request armor support. Around 15:00, Panzer Division Kempf brought its tanks of Panzer Regiment 7 to bear against Uniszki Zawadzkie, folllowed by dismounted Waffen-SS infantry. The attack was slowed when the tanks encountered an anti-tank ditch which the SS infantry had failed to properly report to the armored formations. As Panzer Regiment 7 attempted to find a different path of approach, the German tanks moved laterally across the Polish artillery line and suffered seven tanks (of types Panzer I and Panzer II) lost. This surprisingly high loss of armored vehicle caused Werner Kempf of Panzer Division Kempf to pessimistically report to 3rd Army commander Georg von Küchler that an attack in this sector was hopeless.
On 2 September, Küchler aimed to overcome the obstacles encountered on the previous day by ordering Corps Wodrig to undertake concentrated attacks against the Polish right flank, while I Army Corps was tasked with the continued application of pressure against the main body of the Polish 20th Infantry Division. At the same time, Sturzkampfgeschwader 1 supported German offensive operations with bombing runs against Polish trenches. Two probing attacks by 11th Infantry Division in the afternoon towards the Polish 80th Infantry Regiment were repulsed by dug-in Polish defenders; a similar fate befell an evening strike by 61st Infantry Division against the Polish 78th Infantry Regiment. Meanwhile, Corps Wodrig had made better progress in its flank attack, as the 1st Infantry Division forced the Polish 79th Infantry Regiment into a general withdrawal and the 12th Infantry Division pushed back the Masovian Cavalry Brigade. As a result, 3rd Army commander Küchler now estimated the Polish right flank between Rzegnowo and Przasnysz to be weaker.