The battle of Dermbach (4 July 1866) was a Prussian victory over a Bavarian army that prevented the Bavarians from joining up with their German allies (Austro-Prussian War, 1866). At the start of the war the Prussians were faced with three separate German forces - the Bavarian Army, the Hanoverian Army and the 8th Federal Corps. The Prussians allocated three divisions under General Falckenstein to this campaign, but he was still outnumbered by two-to-one. His biggest advantage was that his three opponents started the campaign widely spread out. The Hanoverians started at Göttingen. The 8th Corps was at Frankfurt and the Bavarians were at Bamberg.
The first fighting came in Hanover. The Hanoverian army made a half-hearted attempt to move south to join up with its allies, but despite winning the only significant battle of the campaign at Langensalza (27 June 1866), they were surrounded and forced to surrender on 29 June. This meant that the Bavarian and 8th Corps plan to unite at Hersfeld, south of Cassel, was no longer relevant. By this point the Federal troops were still close to Frankfurt and the Bavarians had reached Meiningen. The two commanders decided to meet up at Fulda, west of the Bavarians and north-east of the Federal position. The Bavarians were nearest to Fulda, but they would have to cross the Hohe-Rhön Mountains to get there.
On 2 July the Prussians began to move south, heading towards Fulda. On 3 July the Prussians advanced with Beyer's Division in the lead. Goeben's Division was to follow behind and to the left, with orders to clear out any Bavarian troops approaching from the east. Manteuffel's Division formed the rearguard.
The Bavarians were moving west in two columns. Three divisions moved west through the mountains, while Hartmann's Division was sent around the northern flank of the mountains, on a road that led north-west towards Dermbach then south-west towards Fulda. On 3 July Hartmann's advancing troops discovered that the Prussians had already occupied Dermbach in some strength. They also found Prussian troops further east, at Wiesenthal, but they retreated as the Bavarians advanced. By the end of the day the Bavarians had occupied Wiesenthal and also moved troops to Zella, south of Dermbach.
On 4 July General Goeben launched attacks on both Bavarian positions. General Ferdinand von Kummer was sent south to attack the troops at Zella, commanded by General Friedrich von Zoller. General Karl von Wrangel was sent east to attack the troops at Wiesenthal, commanded by General Hartmann in person.
In the south the Prussians attacked Zella from the north and the west, and soon forced the Bavarians out of the village. Soon after this they captured the village of Neidhartshausen, a little further to the north-east. The remaining Bavarians retreated further south to join Zoller's main force at Diedorf. The Bavarians attempted to recapture Zella, but without success.
In the east Wrangel's men forced the Bavarians out of Wiesenthal. The Bavarians took up a new position on a hill called the Nebelberg, west of the village of Rossdorf. Bavarian reinforcements under General Cella reached the battlefield, but the Bavarians were forced to retreat when two Prussian battalions, with a third in reserve, attacked the hill. Hartmann himself led in fresh Bavarians reinforcements, and almost managed to recapture the hill. Finally the Prussians committed fresh troops and the Bavarians were forced to retreat back to Rossdorf.
Goeben's job was to screen the march of the main army towards Fulda, and so in mid-afternoon he called all of his troops back to Dermbach. General Falckenstein decided to abandon the move on Fulda, and instead take what appeared to be a chance to attack the entire Bavarian Army. He called Beyer back from the Fulda Road, moved up his reserves, and prepared to attack. However by the time the Prussians were ready to move, the Bavarians had already decided to retreat. It was clear that the Prussians had advanced much further than expected, and there was no longer any chance of uniting at Fulda.
Further to the south-west Beyer's leading troops had clashed with the Bavarian Reserve Cavalry around Hunfeld. The Bavarians ended up retreating past Fulda, ending any chance of uniting the two German forces there. Both forces began to retreat south, allowing the Prussians to defeat them individually.
Prince Charles of Bavaria ordered his army to retreat south. He still hoped to join up with the 8th Corps south of the mountains, but as both armies moved south news reached them of the crushing Prussian victory at Königgrätz. With the Austrians almost certainly out of the war, the various contingents of the 8th Corps began to concentrate on defending their own homelands. The Bavarians suffered another defeat at Kissingen (10 July 1866), but continued to resist the Prussian advance.