On 8 December 1740, Amboise entered the
French Royal Army as a musketeer and saw extensive service in the
War of the Austrian Succession, beginning with the 1742 campaign in
Flanders. By commission of 1 January 1743, he raised a company in the Royal-Poland cavalry regiment, which he commanded at the recapture of Weissemberg and the lines of the Lautern, at the Haguenau affair on 25 August 1744 and at the siege of
Freiburg im Breisgau on 11 October 1744. On 14 December 1744, he obtained the post of second cornet of a company of the light horses of
Brittany, and the rank of lieutenant-colonel of cavalry. He was at the
Battle of Fontenoy on 11 May 1745, at the sieges of
Tournay,
Dendermonde,
Oudenarde and
Ath in 1745. On 1 December 1745, he joined the company of Gendarmes de Berry, and he participated with this unit at the sieges of
Mons,
Charleroi,
Namur and at the
Battle of Rocoux on 11 October 1746. ==French Revolution==