Napoleon I had been unprepared for the start of hostilities on 10 April 1809, by the Austrians under Archduke Charles of Austria and for the first time since assuming the French Imperial Crown had been forced to give up the strategic initiative to an opponent.

More importantly, unbeknownst to Napoleon, the Austrians gained a victory of their own on 20 April 1809, by surrounding and capturing the French garrison at Regensburg and its strategic bridge over the Danube.

With the seizure of the bridge at Regensburg, Archduke Charles no longer needed to defend the Landshut bridgehead and instead moved to concentrate his remaining forces so as to envelop and destroy Davout's corps.

The mop-up of what Napoleon thought was a "curtain of three regiments" was left to Davout, even though more than half of the III Corps' original units had been detached to create Lannes' task force.

[5] The leading elements of the Austrian attack ran into Montbrun's determined cavalry, who managed to reduce the impetus of the charge thanks to hilly and wooded terrain.

Napoleon had set the French army into motion around 2 a.m. on the 22nd and had his men march 18 miles north in just a few short hours, meaning reinforcements for Davout would be arriving faster than promised.

The vanguard of the assault were the German troops under General Vandamme; these soldiers stormed the bridge at Eckmühl and even captured the town's chateau after ferocious Austrian resistance.

The famous 10th Legere Regiment became involved in vicious fighting around the woods, but eventually was strengthened by Bavarians under Deroy and managed to capture the positions.

North of Unterlaichling, Davout's troops under Louis Friant and St. Hilaire steadily pushed back the defenders of Oberlaichling and the surrounding woods, overran a redoubt held by Hungarian grenadiers, and prompted Charles to order a general retreat.

Nevertheless, the French inflicted 10,700 casualties at the cost of just 3,000, and Napoleon's speedy arrival witnessed an entire axial realignment of his army (from a north–south axis to an east–west one) that permitted the defeat of the Austrians.