 When in 1806 the first British Invasion came to Buenos Aires, he put his fortune at the service of the creole reconquest, organizing a group of conspirators and joining with other groups formed and funded by other prominent merchants, such as Sáenz Valiente and Juan Martín de Pueyrredón.The invading General Beresford had ordered the confiscation of all arms in civilian's hands, but Álzaga who was a specialist in arms smuggling collected hundreds and installed secret gun-repair shops.He rented houses around the main square (Plaza Mayor) in secret, and from there they excavated tunnels to mine the Fort.