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.

[4]: 114  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.

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.

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.

The redeployment and assembly of the unit took until the afternoon of 3 September, partially because of a traffic jam caused by the bulk of the German 1st Cavalry Brigade, which busied itself watering its horses in the center of Chorzele village.

The 8th Infantry Division's counterattack was poorly organized and proceeded without sufficient flank cover, with broken communications and involved numerous friendly-fire incidents between Polish units.

The Germans attempted to prevent the withdrawal of the 8th and 20th Infantry Divisions along the Mława–Modlin road; Luftwaffe air raids caused significant Polish losses in manpower and materiel.

The advance of the 11th and 61st Infantry Divisions was very slow, which gave the Polish garrison of Modlin Fortress an additional five days to prepare their defensive positions.

The Polish supreme commander, Edward Rydz-Śmigły, threw the Polish northern flank into some disarray on 6 September by mistaking this slow advance for an already-completed encirclement of the Modlin Fortress, and ordered the fortress to adopt a circular defensive tactic while ordering a counterattack by Operational Group Wyszków (which, unbeknownst to Rydz-Śmigły, instead faced the majority of German forces on the northern flank) across the Narew river.

Rydz-Śmigły again misjudged the situation and believed the 1st Legions Division to be heavily threatened by annihilation; accordingly, he ordered the city abandoned.

Corps Wodrig had spent a good amount of time on 6 September after the Polish withdrawal from Różan preparing to attack an empty town; meanwhile, the Waffen-SS forces of Panzer Division Kempf of I Army Corps used a lull in combat activity to massacre 50 Jewish civilians in the village of Krasnosielc.

[3]: 248 On 13 September, von Bock directed Küchler to use the forces of I Army Corps to assist in the completion of the encirclement of the Polish capital city, Warsaw, using the 11th and 61st Infantry Divisions as soon as possible.

In the night of 13/14 September, surviving elements of the Polish Modlin Army reached Warsaw and joined the city's defense.[3]: 288f.

At noon, I Army Corps resumed its attacks against the city's northeastern districts, but attained only very limited progress and suffered several local Polish counterattacks.

Although von Bock believed himself victorious, Kutrzeba visited 8th Army in Rakowiec on 28 September at 13:00 to sign the terms of surrender.[3]: 316f.