He later transferred his loyalty to the Kingdom of Prussia and fought during the French Revolutionary Wars, earning a coveted award for bravery.

Cut off from the main body of the Prussian army after the disaster at the Battle of Jena-Auerstedt, he concentrated his troops in the fortress of Hameln.

In 1792 he joined the staff of Feldmarschall Charles William Ferdinand, Duke of Brunswick and fought in the War of the First Coalition at the Battle of Valmy and other actions.

For his courageous actions during the Siege of Mainz from 14 April to 23 July 1793, Lecoq was awarded the Pour le Mérite.

Lecoq was promoted to Oberstleutnant and appointed Brunswick's Quartermaster General, the equivalent of Chief of Staff.

[1] Inspired by the French cartographer Dominique, comte de Cassini, Lecoq completed his Große Karte von Westfalen (Great Map of Westphalia) between 1795 and 1805.

Already celebrated as a talented map-maker in his own right,[1] the king named him commander-in-chief of the Grenadier Garde Infantry Regiment Nr.

[7] Opposing them were King Louis Bonaparte, leading the army of the Kingdom of Holland, and Marshal Édouard Adolphe Casimir Joseph Mortier at the fortress of Mainz.

[8] Emperor Napoleon I of France intended for the forces of Louis and Mortier to observe the Prussians until he defeated their main army.

Ten days later, news of the catastrophic Battle of Jena-Auerstedt reached Lecoq and he immediately ordered a retreat.

Napoleon knew that William I, Elector of Hesse, though officially neutral, was pro-Prussian and he determined to depose him.

[10] Mortier's 5,500 men and Louis' troops overran Hesse-Kassel, disarmed the Hessian army, and chased the elector into exile.

Mortier left 6,000 men to maintain the Siege of Hameln and continued his march[12] on Hanover, which he occupied on 12 October.

[13] Jean Baptiste Dumonceau commanded the Hameln blockading force which was organized into one cavalry and three infantry brigades with 12 artillery pieces.

[14] While these operations were in progress, Napoleon signed an armistice with the king's envoy Girolamo Lucchesini that specified that the remaining Prussian fortresses were to be surrendered.

King Frederick William III later refused to sign the document, but that did not stop the French emperor from trying to exploit the tentative agreement.

He sent Anne Jean Marie René Savary to Hameln with the information in an attempt to coax the garrison into laying down its arms.

The surrender terms were similar to those at the Capitulation of Prenzlau in that officers were to be paroled and the enlisted men were to be made prisoners.

[12] When Lecoq's rank and file found out about the capitulation, a mutiny broke out and the soldiers forced their way into wine-shops and soon became drunk.

[17] Francis Loraine Petre believed that Lecoq's situation was hopeless, but that it was his responsibility to hold out as long as possible.

In 1814 he was finally pardoned and took up residence in Berlin where he continued work on his beloved maps as his eyesight faded away.