 He was sent to study at the Royal College of San Carlos in Buenos Aires.At 23 he started his military career and took part in the defense of Buenos Aires during the British invasions of the Río de la Plata, where Güemes achieved notability when he and his cavalrymen charged and took over the armed British merchantman "Justine", moored in shallow waters.After the formation of the first local government junta in the May Revolution of 1810, he joined the army destined to fight the Spanish troops at the Upper Peru, which was victorious in the Battle of Suipacha (in present-day Bolivia).