In the campaign of 1805, he led an infantry division under Marshal Pierre Augereau in Emperor Napoleon's Grande Armée and saw limited fighting.

Born on 9 February 1759 in Angers, France, Desjardin joined the French army on 8 December 1776 at the age of 17.

Since his father worked as a humble valet, Desjardin's prospects of advancement in the Vivarais Infantry Regiment were poor.

He was granted leave to see his father in 1790 and immediately threw himself into the task of drilling his hometown National Guard unit.

During the siege, Desjardin's battalion served in the Left Brigade of Louis-Auguste Juvénal des Ursins d'Harville's Reserve Division.

One political agent attached to the army remarked, "I did not see the shadow of treason, but the incapacity of the leaders was flagrant".

[5] For the next attempt, the army was to be guided by a council of Generals Desjardin, Charbonnier, Jean-Baptiste Kléber and Barthélemy Louis Joseph Schérer.

[7] On 24 May in the Battle of Erquelinnes, Kaunitz launched a pre-dawn attack in five columns, catching Desjardin's troops completely by surprise and capturing hundreds of sleepy French soldiers.

Total disaster was averted when Kléber heard cannon fire and countermarched, helping to slow the Allied pursuit.

On 3 June, a 28,000-man Austro-Dutch relief force under William V, Prince of Orange defeated him in the Battle of Gosselies, inflicting 2,000 casualties on the 27,000 French who were present and capturing one 12-pound cannon.

[1] On 28 February 1804, the soon-to-be Emperor Napoleon made Desjardin a member of the Légion d'Honneur and recalled him to military service at Brest.

[16] Having a long march from Brest to the Danube at the start of the War of the Third Coalition, Augereau's corps missed the Ulm Campaign in October 1805.

While the main army was headed for a showdown at the Battle of Austerlitz, the VII Corps operated against enemy troops in the Vorarlberg.

Three generals, 160 officers, and 3,895 rank and file laid down their arms and were permitted to march to Bohemia where they were not to undertake operations against France for one year.

[18] At the beginning of the War of the Fourth Coalition, Desjardin still commanded the 1st Division of the VII Corps, a total of 8,242 soldiers and eight artillery pieces.

[19] At the Battle of Jena, Augereau's corps formed the left flank as Napoleon engaged the Prussian-Saxon army of Frederick Louis, Prince of Hohenlohe-Ingelfingen.

[21] When Ernst von Rüchel made his belated and futile attack after 1:00 PM, it was opposed by the artillery of Desjardin, as well as the guns of Marshals Nicolas Soult, Michel Ney, and Lannes.

[22] Meanwhile, Augereau's main assault fell on Zeschwitz's Saxons and a supporting Prussian brigade under Karl Anton Andreas von Boguslawsky.

Seeing an opportunity, Marshal Joachim Murat led Louis Klein's dragoons to take the Saxons in the rear while Jean-Joseph Ange d'Hautpoul's cuirassiers attacked their left flank.

[28] Also on the 24th, Augereau directed his two divisions to force a crossing of the Wkra River in the face of nine Russian infantry battalions and five cavalry squadrons under Michael Andreas Barclay de Tolly.

Aided by Lapisse's task force which crossed 3 kilometres (1.9 mi) downstream, Desjardin's men drove off the Russians and captured six cannons.

The large French numerical advantage was partly offset by the fact that Golitsyn had taken up an excellent defensive position.

[37] Around 9:00 AM, Napoleon ordered Soult to attack on the left, but his two divisions were thrown back by the Russians after a terrific struggle.

Historian David G. Chandler suggested that Augereau should have formed his men in battalion columns in the prevailing weather conditions.

Not only did this create a dangerous gap on Augereau's right flank, but it sent his men marching blindly into range of a 70-gun grand battery in the center of the Russian line.

[37] The Russian commander Levin August, Count von Bennigsen, sent his reserves to counterattack the badly disordered French infantry.

That evening, the acting VII Corps commander Jean Dominique Compans reported that only 700 men were with the colors from each of the divisions.