The battle of Pirna (26 August 1813) was a key part of Napoleon's plan to win a major victory at Dresden, and saw Vandamme attempt but fail to cut off the Allied lines of retreat from Dresden back into Bohemia.
At the start of the Autumn Campaign of 1813 the first of the Allied armies to move was Blücher's Army of Silesia, which began to threaten the eastern border of Saxony. Napoleon had taken up a central position, from where he could strike whichever Allied army moved first, and so he decided to lead a large part of his army east to attack Blücher.
Napoleon's plan was frustrated by two factors. First was the Trachenberg Plan, in which Blücher was forbidden to risk fighting Napoleon in person. The second was that the main Allied Army of Bohemia began an advance on Dresden. Marshal St. Cyr, defending the city, realised that he would be unable to defend it without help, and sent messengers to Napoleon with the news.
Napoleon realised that he had a chance to inflict a major defeat on the Army of Bohemia. He could cross the Elbe upstream of Dresden and cut the Allied lines of communication back to Bohemia, forcing them into a disastrous retreat away from their base or a battle on his terms. However as he got closer to the Elbe, the news from Dresden was worrying. Napoleon had to abandon his original plan for a large scale crossing of the Elbe to the south-east of Dresden, and instead decided to lead most of his army back to the city, while Marshal Vandamme, with a single corps, was left to carry out the crucial outflanking movement.
On 26 August (the first day of the battle of Dresden) Vandamme crossed the Elbe by the bridges at Königstein, under cover of the Königstein fortress, east of Pirna. By 5pm he had 34 infantry battalions and Corbineau's cavalry across the river.
He faced a smaller observing force under Prince Eugène of Wurtemberg.
Vandamme attacked west towards Eugène around Pirna. Prince Eugène was able to hold out until dark, but then had to retreat from the Pirna town and plateau. He retreated to a new position to the north and south of Zehista, facing towards the Elbe, and sent urgent messages asking for reinforcements. The Allied high command responded by replacing him with Ostermann-Tolstoy, who was ill at the time.
Eugène's retreat meant that the Allies could no longer use the Peterswalde road, the best link between their Bohemian bases and the army at Dresden.
On 27 August Vandamme wasn't terribly active. Part of his corps was still crossing the river during the morning. Mouton-Duvernet's 42nd Division (borrowed from St. Cyr's corps) occupied Pirna and the Pirna plateau, abandoned by the Allies overnight. Phillipon's division was placed to the left of Krietschwitz (south-east of Pirna). Corbineau's cavalry moved to an area between Langen Hennersdorf and Berggieshübel, south-east of Krietschwitz and south-west of Königstein.
Vandamme was unsure of the strength of the Allied forces opposing him, and believed that he needed his entire corps to be able to attack. As a result he made little progress during the day. At about 4pm news of the French success at Dresden reached him, and he issued ordered for a move south to Berggieshübel and Hellendorf on the following day. Vandamme's lack of action on 27 August helped robbed Napoleon of the benefits of his great victory at Dresden. If he had been more resolute, the retreating Allies might have found their road to safety blocked. As it was they struggled to get to safety. Vandamme would soon compound his error - on 29-30 August he suffered an major defeat at Kulm, when he got trapped between two parts of the retreating Allied army and had to surrender.