The Allied Army and Plan
The French Armies
The battle of Valmy, 20 September 1792, was the first major battle of the War of the First Coalition, and saved the infant French Republic from early destruction. Ever since the start of the French Revolution France's neighbours had been watching events in Paris with increasing alarm. On 2 August 1791 in the Declaration of Pillnitz the king of Prussia and the Austrian Emperor had declared their intention of forming an alliance to restore the authority of the Bourbons in France. An official Austro-Prussian alliance had been formed on 7 February 1792, and Allied armies had begun to form on France's eastern borders, but the actual declaration of war came from the French, on 20 April 1792.
An early French invasion of the Austrian Netherlands ended in embarrassing failure (see battle of Baisieux), and the French army was generally believed to be in a terrible condition. Many of the best officers had fled France, forming the group known as the émigrés, who began to plot against the revolution from safe havens just across France's eastern borders. The troops no longer trusted the officers who remained, and a cry of 'betrayal' could easily lead to mass panic and the murder of any suspect commander. The Austrians and Prussians were confident that they would sweep aside the French armies and restore Louis XVI.
The Allied Army and Plan
Different sources give different figures for the size of the Allied army, but all fall in roughly the same range. The Prussians provided 40,000-42,000 men and the Austrians 29,000-30,000. This army was supported by 5,000 Hessians and somewhere between 8,000 and 15,000 French émigrés, who made up an enthusiastic, experienced but unreliable (or unpredictable) cavalry force. The fighting at Valmy would only involve 30-34,000 of the Prussians.
The combined army was commanded by Karl Wilhelm Ferdinand duke of Brunswick, an experienced Prussian field marshal, but his position was undermined by the presence of King Frederick William II of Prussia with the army. The two men had very different ideas for the upcoming campaign, with Brunswick wanting to establish a strong base on the French border in 1792 in preparation for an invasion in 1793, while Frederick William favoured a bolder policy.
The eventual Allied plan was to invade France from Coblenz, capture the border fortresses of Longwy and Verdun, and then advance towards Paris via Châlons. The Austrians and Prussians confidently expected to sweep aside the French armies opposing them, which they incorrectly believed to be made up of a revolutionary rabble.
The French Armies
The Allied invasion was opposed by two of the three French armies on the eastern border – the Armée de Nord and the Armée du Centre. The command of both of these armies changed at the start of the invasion. At the start of the war in April 1792 the armies had been commanded by two veterans of the American War of Independence, Lafayette in the centre and Rochambeau in the north. Rochambeau resigned early in the war, after the embarrassing failure of an early invasion of Belgium (then the Austrian Netherlands). Lafayette became increasingly disenchanted with the radical direction the revolution was taking in Paris. After an attempt to rescue the king's position on 28 June he returned to his army, but an attempt to rally support after the fall of the monarchy on 10 August failed, and he fled into Austrian custody.
The new commanders arrived in mid august. On 16 August General Charles François Dumouriez took command of the Army of the North, while on 27 August General François Etienne Christophe Kellermann took over the Army of the Centre. The two French armies were made up of soldiers from the old Royal army, with a sprinkling of volunteers. At Valmy it would be the experienced Royal artillery that would win the day.
The Allied invasion began on 19 August. Longwy fell on 23 August and Verdun on 2 September, but progress was slow. Brunswick favoured a slow but steady advance, but came under increasing pressure from King Frederick William to speed up, especially as the position of Louis XVI became increasingly precarious.
The French Government responded to the invasion by ordering Dumouriez to abandon his planed invasion of the Austrian Netherlands and move south to block the Allied invasion. At the start of September Dumouriez took up a position in the Argonne Forest, blocking the main passes through the area. He described this position as France's Thermopylae, and perhaps rather ironically this position was also bypassed when the Allies captured a lightly defended pass at Croix-aux-Bois, towards the northern end of the French line. Dumouriez retreated west to Valmy and Sainte-Manehould, on the western side of the Argonne Forest, to a position from where he could block the best road back across the Argonne to Germany and the Allied supply depots. On 19 September Dumouriez was joined by Kellerman, who had been ordered to move north some days earlier.
The Allied army passed through the Croix-aux-Bois, and then turned south to confront the French. The battle of Valmy was thus fought with the Allies attacking towards the east, with their backs towards Paris, and the French facing west, between the Allies and Germany. Brunswick could have risked a dash on Paris, but that was not his style of warfare. Instead he decided to attack the French at Valmy in an attempt to clear the road back to Germany.
The two French armies took up a position on the hills around Valmy. Kellerman, with the largest part of the army (around 36,000 men), took up a position west of Valmy, on a ridge topped by a large windmill, while Dumouriez, with 18,000 men, formed a second line to the east of the village.
Brunswick, with his Prussians, took up a position on another line of hills 2,500 yards to the west of Kellerman's position. A long range artillery duel followed, with neither side suffering significant casualties. The French army held its ground under fire, beginning to prove that it was still a force to be reckoned with. Eventually Brunswick ordered his troops to advance, perhaps expecting the French infantry to break once the famous Prussian infantry was on the move. When the French still stood their ground, Brunswick cancelled this first attack and the artillery duel recommenced.
A second, and slightly more determined Prussian attack was made after a lucky shell hit one of the French ammunition wagons, causing a large explosion. This time the Prussian infantry reached within 650 yards of the French, and began to suffer some casualties, before Brunswick once again called off the attack. Finally, at 4.00pm he abandoned the battle. Neither side suffered heavy casualties in the artillery duel – Prussian casualties came to 164, French to around 300 (although a range of different figures exist, all fall in the same low ranges).
The two armies remained in the vicinity of Valmy for the next ten days. Dumouriez attempted to open negotiations with the Prussians, in the hope that he could detach them from the Alliance against France, but on the day after the battle France officially became a Republic. Frederick William demanded the restoration of the monarchy as a first step towards peace, and in return the French demanded that the Prussians evacuate all French territory before negotiations could continue. Unsurprisingly negotiations were then broken off, and on the night of 30 September-1 October the Allied army began its retreat back towards the French border, crossing out of France on 23 October. By then Verdun and Longwy were already back in French hands, and the immediate danger to the Republic was removed.
The battle of Valmy ensured the continuation of the French Revolution. In its aftermath Dumouriez was free to carry out his invasion of the Austrian Netherlands, where he won a second important victory at Jemapes (6 November 1792). The Prussians would soon withdraw from the war, to concentrate on events in Poland. France was threatened by invasion again in 1793, but her enemies had missed their best chance to destroy the Republic.