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Military service

In June 1791, Louis Philippe got his first opportunity to become involved in the affairs of France. In 1785, he had been given the hereditary appointment of Colonel of the Chartres Dragoons (renamed 14th Dragoons in 1791).

With war imminent in 1791, all proprietary colonels were ordered to join their regiments. Louis Philippe was a model officer, and demonstrated his personal bravery in two famous instances. First, three days after Louis XVI's flight to Varennes, a quarrel between two local priests and one of the new constitutional vicars became heated. A crowd surrounded the inn where the priests were staying, demanding blood. The young colonel broke through the crowd and extricated the two priests, who fled. At a river crossing on the same day, another crowd threatened to harm the priests. Louis Philippe put himself between a peasant armed with a carbine and the priests, saving their lives. The next day, Louis Philippe dived into a river to save a drowning local engineer. For this action, he received a civic crown from the local municipality. His regiment was moved north to Flanders at the end of 1791 after the 27 August 1791 Declaration of Pillnitz.

Louis Philippe served under his father's crony, Armand Louis de Gontaut the Duke of Biron, along with several officers who later gained distinction. These included Colonel Louis Alexandre Berthier and Lieutenant Colonel Alexandre de Beauharnais (husband of the future Empress Joséphine).

After the Kingdom of France declared war on the Habsburg monarchy on 20 April 1792, Louis Philippe first participated in what became known as the French Revolutionary Wars within the French-occupied Austrian Netherlands at Boussu on about 28 April 1792. He was next engaged at Quaregnon on about 29 April 1792, and then at Quiévrain near Jemappes on about 30 April 1792. There he was instrumental in rallying a unit of retreating soldiers after French forces had been victorious at the Battle of Quiévrain (1792) two days earlier on 28 April 1792. The Duke of Biron wrote to War Minister Pierre Marie de Grave, praising the young colonel, who was promoted to brigadier general; he commanded the 4th Brigade of cavalry in Nicolas Luckner 's Army of the North.

In the Army of the North, Louis Philippe served with four future Marshals of France: Étienne-Jacques-Joseph-Alexandre MacDonald, Édouard Adolphe Casimir Joseph Mortier (who would later be killed in an assassination attempt on Louis Philippe), Louis-Nicolas Davout and Nicolas Oudinot. Charles François Dumouriez was appointed to command the Army of the North in August 1792. Louis Philippe continued to command his brigade under him in the Valmy campaign.

At the 20 September 1792 Battle of Valmy, Louis Philippe was ordered to place a battery of artillery on the crest of the hill of Valmy. The battle was apparently inconclusive, but the Austrian- Prussian army, short of supplies, was forced back across the Rhine. Dumouriez praised Louis Philippe's performance in a letter after the battle. Louis Philippe was recalled to Paris to give an account of the Battle at Valmy to the French government. He had a rather trying interview with Georges Danton, the Minister of Justice, which he later told his children about. Shortly thereafter, he was made Governor of Strasbourg.

While in Paris, he was promoted to the rank of lieutenant general. In October Louis Philippe returned to the Army of the North, where Dumouriez had begun a march into the Austrian Netherlands (now Belgium). Louis Philippe again commanded a brigade, even though he held the rank of lieutenant general. On 6 November 1792, Dumouriez chose to attack an Austrian force in a strong position on the heights of Cuesmes and Jemappes to the west of Mons. Louis Philippe's division sustained heavy casualties as it attacked through a wood, and retreated in disorder. Lt. General Louis Philippe rallied a group of units, dubbing them "the battalion of Mons", and pushed forward along with other French units, finally overwhelming the outnumbered Austrians.

Events in Paris undermined his budding military career. The incompetence of Jean-Nicolas Pache, the new Girondist appointee of 3 October 1792, left the Army of the North almost without supplies. Soon thousands of troops were deserting the army. Louis Philippe was alienated by the more radical policies of the Republic. After the National Convention decided to put the deposed King to death, Louis Philippe began to consider leaving France. He was dismayed that his own father, known then as Philippe Égalité, voted in favour of the execution.

Louis Philippe was willing to stay to fulfill his duties in the army, but he became implicated in the plot Dumouriez had planned to ally with the Austrians, march his army on Paris, and restore the Constitution of 1791. Dumouriez had met with Louis Philippe on 22 March 1793 and urged his subordinate to join in the attempt.

With the French government falling into the Reign of Terror about the time of the creation of the Revolutionary Tribunal earlier in March 1793, Louis Philippe decided to leave France to save his life. On 4 April, Dumouriez and Louis Philippe left for the Austrian camp. They were intercepted by Lieutenant-Colonel Louis-Nicolas Davout, who had served at the Battle of Jemappes with Louis Philippe. As Dumouriez ordered the Colonel back to the camp, some of his soldiers cried out against the General, now declared a traitor by the National Convention. Shots rang out as the two men fled toward the Austrian camp. The next day, Dumouriez again tried to rally soldiers against the convention; however, he found that the artillery had declared itself in favour of the Republic. He and Louis Philippe had no choice but to go into exile when Philippe Égalité was arrested.

At the age of nineteen, and already ranked as a Lieutenant General, Louis Philippe left France. He did not return for twenty-one years.