Adam Philippe, comte de Custine (1704-1793) was one of a number of early French commanders during the War of the First Coalition to be executed for treason as a result of military failures. Like many generals in the early revolutionary armies Custine was an aristocrat, the son of Philippe François Joseph, comte de Custine.
Custine joined the army as a lieutenant on 16 September 1747. He fought as a captain during the Seven Years War. In 1762 the influence of the Duke of Choiseul got him command of a regiment of Dragoons. In 1780 he exchanged this for the regiment of Saintonge, which he then commanded in American during the War of American Independence. On 5 December 1781 he was promoted to brigadier, and in April 1782, after his returned from the United States, he was appointed commander of Toulon.
Custine was one of many noblemen whose experience in American made them sympathetic to the Revolution. On 16 March 1789 he was elected to the Estates General as the representative of the nobility of Metz, and he soon came out in favour of reform.
On 6 October, after the end of his term in the Estates General, Custine was promoted to lieutenant general, and in the following year he became the field commander of the Army of the Rhine, under the overall command of General Biron. At the start of the War of the First Coalition Custine commanded 15,000 men at Landau. While France was threatened by invasion, Custine used his small army to occupy the left bank of the Rhine. He entered Spires (Speyer) on 30 September, only nine days after the Allied invasion had been turned back at Valmy, and before the Duke of Brunswick had actually begun his retreat back towards the French border. He then went on to take Worms (5 October), and most impressively Mainz (19-21 October).
Custine's ambitions now got the better of him, and he decided to plunge east into Germany. On 27 October 1792 he captured Frankfort, but this unfortified neutral commercial city was impossible to defend without support from larger French armies, and that support was not forthcoming. Over the next month Custine levied a financial contribution from the city, and generally turned the population against the French, before on 2 December the Duke of Brunswick forced him to retreat west to Mainz.
In the aftermath of this retreat Custine offered his resignation to the Convention, but it was refused, and he was left to defend the Rhine. During this period on the Rhine Custine was partly responsible for beginning the careers of the further marshals St. Cyr and Soult. St. Cyr was promoted to his staff after Custine noticed him sketching enemy positions, while Soult was used on a number of dangerous scouting missions.
In March 1793 the Prussians crossed the Rhine. Custine was at Worms when the attack began. He advanced to the front, but was then discouraged by some early setbacks, and pulled back to Landau, claiming to be massively outnumbered. The Allies were left to besiege Mainz (14 April-23 July 1793) almost without interference, although in mid-May Custine did make one attempt to attack the covering force.
Custine was now beginning to fall foul of the radicals in the Convention, amongst them Marat who began to attack him as a second Dumouriez, using his position in the army to help the enemies of France. Unlike Dumouriez, Custine was not involved in any such activities, but his failures and his aristocratic birth made his suspect. His fall from power was probably only a matter of time, but he would gain one further promotion before then.
On 8 May General Dampierre, the commander of the Army of the North, was fatally wounded. The Committee and Executive Council of the Convention promoted General Kilmaine to the post, but this was overruled by the Convention, and on 13 May Custine was given the task instead. He arrived at Cambrai on 27 May, and then began the difficult job of restoring the morale and organisation of the army. That reorganisation played a part in Custine's fall. Politically radical but militarily useless officers agitated in Paris, where Custine's failure to raise the sieges of Condé or Valenciennes took the shine off his already tarnished military reputation.
On 22 July the Convention decided to arrest Custine. Condé had already fallen. On the next day Mainz fell, and Valenciennes soon followed. Even though Custine was no longer in command on the Rhine the fall of Mainz was seen as proof of his treachery. He was found guilty of treason, and on 28 August 1793 was executed.