At the end of the war he formally entered the Austrian army, joining the Hesse-Darmstadt Dragoon Regiment # 19 as an
Oberleutnant. Promoted to
captain in 1769 and
major in 1777, he transferred to the Graeven Hussar Regiment # 34. Because he improved his new regiment's efficiency, he was rapidly promoted, first to
Oberstleutnant in 1783 and
Oberst in 1784. In the
Austro-Turkish War (17881791), he led his regiment in action at
Chernivtsi and Cornia. Promoted to
General-major in 1788, he continued to distinguish himself against the Turks. In 1793 during the
War of the First Coalition, Otto joined the Austrian army in Flanders, serving at the siege of
Valenciennes. At the battle of Caesar's Camp on 7 August, he commanded an infantry-cavalry brigade in the
Count of Clerfayt's column. On 12 September he participated in the cavalry action at
Avesnes-le-Sec in which a French force was cut to pieces. On 30 October he led his troops in battle at
Marchiennes. He was promoted to
Feldmarschal-Leutnant on 1 January 1794 and also became proprietor (
inhaber) of the Hussar Regiment # 32. On 24 April, while leading two Austrian and two British cavalry squadrons on a reconnaissance toward
Cambrai, Otto encountered a force of French cavalry. At this time, he discovered that
Emperor Francis II was nearby with his retinue. Fearing that his sovereign was about to be captured, he resolved to attack the enemy. In the ensuing
Battle of Villers-en-Cauchies, Otto's troopers smashed a 7,000-man French division, inflicting 1,200 casualties. Two days later, Otto led the main attack in the
Duke of York's victory at
Beaumont, rolling up the French flank and capturing the French commander
René Chapuis. At the
Battle of Tourcoing, he led one of York's three columns. Though the Anglo-Austrian army went down to defeat, Otto performed well. ==Later career==