Five years would pass before the grenadiers' next engagement, which occurred during the War of the Third Coalition. As war broke out with Russia and Austria, the horse grenadiers, now a part of the Imperial Guard, crossed the Rhine into Germany on October 1, 1805. Ten days after that, they were at Augsburg and on October 20 they were present at the surrender of Ulm. They would see their only major action during this campaign on December 2, on the Pratzen plateau, at the battle of Austerlitz. During this battle, Napoleon had planned to break the Austro-Russian centre and thus split their forces. The plan was well under way towards mid morning but a potentially dangerous situation for the French occurred when the Russian Imperial Guard under Grand Duke Constantine arrived and attacked the French from Vandamme's division around Stary Vinohrady ('the old vineyards'). At first, one battalion of the French 4th Line regiment was caught in an awkward position and broken by the Russian Guard cavalry supported by artillery, with the French battalion losing its eagle and over 400 men. Then, the 24th Light regiment, which was coming up in support of the 4th, was also thrown back in disarray. It was at this moment that Napoleon sent in his Guard cavalry: 4 squadrons, 423 men, of the Chasseurs à Cheval and Mameluke regiment and 4 squadrons, 706 men, of the Grenadiers à Cheval regiment, with a battery of Guard horse artillery in support. The grenadiers charged vigorously and clashed with the Russian Chevalier Guard regiment. After a short mêlée, the horse grenadiers broke the opponent, inflicting heavy casualties and capturing over 200 men, their commander - Prince Repnin - with his general staff, as well as 27 pieces of artillery, with the loss of just 2 killed and 22 wounded (among which 6 officers wounded).