The combat of Arnhofen (19 April 1809) was a Bavarian victory over an Austrian brigade guarding the left flank of the main Austrian army during its invasion of Bavaria at the start of the Franco-Austrian War of 1809.
The main focus of the Austrian effort on 19 April was an attempt to isolate Marshal Davout's corps, which was attempting to march west from Regensburg to rejoin the rest of the French army. The two sides clashed at Teugn-Hausen, where the French were able to slip past the much larger Austrian force. At the same time a series of more minor clashes took place around the flanks of the two armies.
When Archduke Charles turned north on 19 April to try and catch Davout, this left his left flank exposed to a possible attack by the Bavarian troops of Marshal Lefebvre's 7th Corps. Charles ordered his III Corps to detach a brigade towards the line of the Abens River, and especially around Biburg and Abensburg.
GM Thierry's brigade of around 6,000 men was chosen for the task. This brigade moved west from the army HQ at Rohr to Kirchdorf, and was then split into several detachments. One infantry battalion and a half squadron of dragoons went to Hörlbach, about one mile to the north-west of Kirchdorf. Another battalion, three and a half cavalry squadrons and four guns were placed close to Bruckhof, another mile to the north-west. Finally Thierry led the remaining two infantry battalions, two dragoon squadrons and four guns north towards Arnhofen, where he believed he might find some Bavarian troops. This took them through a large wooded area, the Seeholz, much of which still exists.
The main road from Abensberg to Regensburg ran past Arnhofen. Crown Prince Ludwig's 1st Bavarian Division was about to pass along this road, heading towards the sound of the guns at Teugn-Hausen, with GM Friedrich von Zandt's cavalry brigade acting as its advance-guard. All of this was hidden from Thierry, who could only see a few Bavarian horsemen on top of some low hills between the road and the woods.
As the Austrians advanced towards the hills Marshal Lefebvre ordered one of his cavalry regiments to turn right off the line of march. Thierry reacted by ordered his own cavalry to charge the newcomers, who rather bizarrely chose to meet this attack standing still, rather than at the charge. Despite support from a Bavarian artillery battery, their cavalry were forced back. Lefebvre was forced to sent his 1st Dragoons into the battle, The two Bavarian cavalry regiments were able to force the Austrians back to the edge of the woods.
A second fight was going on to the west of the woods, where Thierry had posted two infantry battalions to guard against an attack from Abensberg. These battalions managed to provoke just such an attack, led by Lefebvre in person, and after three unsuccessful attempts the Bavarians forced the Austrians to retreat into the woods. Only the arrival of Thierry's reserves restored the situation.
The fighting now expanded on both flanks, and by around 3-4pm Thierry was forced to order a retreat. His brigade rather disintegrated at this point, with half of the infantry retreating south while Thierry and the rest of his brigade moved south-east towards Offenstetten. The Bavarian pursuit was limited, and was anyway ended by the same storm that had forced an end to the fighting at Teugn-Hausen.
The nearest Thierry came to receiving any aid from the rest of the Austrian army was a short-lived advance by GM Friedrich Bianchi's brigade, which was sent in his general direction in mid-afternoon. This tentative advance ended when a single Bavarian infantry regiment advanced towards Bianchi from the west, without ever coming into combat. Even after the Bavarians pulled back to the west, Bianchi's advance came to an end.
On the following day Thierry's brigade would find itself in the front line once again, as Napoleon's counterattack burst onto the disorganised Austrian army (battle of Abensberg).