The next year, the Peninsular war erupted and the "Grenadiers à Cheval", together with two newly created Young Guard infantry regiments and some Guard artillery were a part of Bessières' 2nd Corps of the Army of Spain, and were present in Madrid during the May uprising, where their first surgeon, Gauthier, was wounded. They then campaigned in the north-west of the country. On July 14 Bessières, with around 14 000 men faced two massed Spanish corps of about 22 000 men, not far away from Valladolid. A few squadrons of the regiment saw brief but decisive action in the ensuing battle of Medina del Rio Seco, as they came up in support of general Merle's infantry attack, which repulsed the Spaniards onto Medina and beyond, winning the battle.