The Battle of San Nicolás was a naval engagement on 2 March 1811 on the Paraná River between the Spanish royalists from Montevideo, and the first flotilla created by the revolutionary government of Buenos Aires. It was the first engagement between the two fleets in the Río de la Plata region since the revolution, and a royalist victory. Background On 25 May 1810 the River Plate colonies revolted against the Spanish Viceroy at the May Revolution in Buenos Aires, claiming the necessity of assuming local government due to the difficult situation in Spain, which was occupied by Napoleonic troops. The royalist authorities in Montevideo opposed the measure and declared a naval blockade of Buenos Aires. In the city of Montevideo, there was a navy base serving as port for the royal Spanish fleet in the South American Atlantic coast. The local Junta Grande (Buenos Aires' revolutionary government) decided to establish a fleet to contest the Spanish dominion of the local waters. Creation of the rebel fleet The Junta Grande which took control of the government in Buenos Aires named Francisco de Gurruchaga, as secretary of the Navy. He immediately set to work to create a small naval fleet. With effort, Gurruchaga bought five vessels of different types from local owners, and equipped three of them with artillery, which had been taken for the most part out of service as obsolete. He obtained a schooner, a brigantine and a sloop, christened respectively "Invencible", "25 de Mayo" and "América". Recruiting of the crew was another difficult endeavor, as the inhabitants of the pampas were not used to a sailor's life. The solution was to hire foreigners, who for the most part did not speak Spanish. The rank and file was filled with locals. Command of the flotilla was given to a Maltese privateer, Lieutenant Colonel Juan Bautista Azopardo. This sailor had arrived in the River Plate at the beginning of the 19th century, and had participated in the British invasions of the Río de la Plata of 1806 and 1807. Azopardo commanded the "Invencible", seconded by Hipólito Bouchard on "25 de Mayo", and Ángel Hubac, on "América". The first mission At the beginning of 1811 the Junta Grande was immersed in armed conflicts in various fronts against counter-revolutionary (royalist) forces. A small army under the command of Manuel Belgrano had been sent to Paraguay to help the locals join the revolution, but