In 1812 during the French invasion of Russia, Joseph Napoleon's Regiment was deployed for combat. The 2nd and 3rd battalions formed part of Marshal Davout's I Corps while the 1st and 4th battalions formed part of Prince Eugene's IV Corps. In the 1812 campaign Joseph Napoleon's Regiment fought at Shevardino, forming squares and protected a French infantry regiment that had been attacked and disorganized by Russian cavalry from further cavalry attacks. At the Battle of Borodino all four battalions of Joseph Napoleon's Regiment were present, the 3rd and 4th battalions participated in fighting for the great redoubt that dominated the battlefield at Borondino. Joseph Napoleon's Regiment fought during the French retreat from Russia at Battle of Krasnoi and Battle of Berezina. During this retreat, about 300 soldiers defected from the French in Vilnius and joined the Russian army, where they formed the Imperial Alexander Regiment; they were later transported to Spain to fight the French occupants. In the 1813 campaign in Germany Joseph Napoleon's Regiment fought at Battle of Lützen, Battle of Bautzen, Battle of Leipzig, and Battle of Hanau.