Buenos Aires was involved in the British invasions of the Río de la Plata in 1806, when British forces led by William Carr Beresford captured the city. Saavedra was still a civilian by then. Santiago de Liniers organized an army in Montevideo to re-capture Buenos Aires, and Saavedra was among the civilians that joined Liniers, despite the lack of military instruction. His role in this battle was a minor one. Liniers successfully re-captured Buenos Aires, and organized the city's defences against a likely British counter-attack. All the male population of the city aged from 16 to 50 was drafted into the army, and divided in battalions by casta or origin. The largest one was the Regiment of Patricians, made up of volunteer infantrymen born in Buenos Aires. The Regiment was composed of three infantry battalions, commanded by Esteban Romero, Domingo Urien and Manuel Belgrano, who would later pass that command to Juan José Viamonte. Each battalion could elect their own leaders, including their commander, and the Regiment of Patricians elected Saavedra.