ranks of the Army of the Duchy of Warsaw. Napoleon's invasion of Spain (1808) Pac was involved in Napoleon's invasion of Spain in 1808. During it, Pac distinguished himself militarily, demonstrating courage and military capability, while being the Chief of Staff of Marshal Jean-Baptiste Bessières' I Corps. For example, while commanding a squadron during the Battle of Medina de Rioseco, his horse was killed under him and he was wounded in the thigh by a bayonet thrust but he resumed the assault and pushed the enemy back. On 14 August 1808, Count Pac received the Knight's Cross of the Legion of Honour and was promoted to lieutenant colonel. On August 28, Pac was appointed squadron leader in the 1st Light Cavalry Lancers Regiment of the Imperial Guard. War of the Fifth Coalition (1809) After Spain, Pac fought in the War of the Fifth Coalition against the Austrian Empire in 1809. He fought at the Battle of Aspern-Essling and Wagram. During the latter battle, at the head of the 1st Polish Light Cavalry Regiment, whose colonel he now was, Pac charged Schwarzenberg's cavalry. After the war ended, Count Pac escorts Napoleon back to Paris. 1809–1812 However, Pac disillusioned with Napoleon after his duplicity concerning the Duchy of Warsaw, became indignant and sent his resignation to Napoleon on 19 October 1809, claiming problems of health. Pac went to Warsaw. Soon, Pac returned to military service, and commanded the . Later, Pac regained his confidence in Napoleon and was appointed governor of the Duchy's Łomża Department, where he organized and equipped at his own expense a national guard of 3,000 men, which Pac commanded. Pac also organized a network of informants. French invasion of Russia (1812) During the French invasion of Russia, when the Grande Armée crossed the Nemunas on 24 June 1812, Count Pac rushed to Vilnius to receive the Emperor in the Pac Palace (today the Embassy of Poland in Vilnius). Napoleon, who appreciated this, invites him to dine with Berthier and Maret. On July 14, during the celebration of the reunification of the two nations, Poland and Lithuania, at the Vilnius Cathedral, Count Pac is on Napoleon's left. In the evening, the count gives a grand ball in another of his palaces (now located at Didžioji Street 7) in which the civil and military authorities, both Lithuanian and French, partook. Prince Joachim Murat, King of Naples resided at the time