was composed of eleven warships. British , paddle (6 guns, Capt. Charles Hotham) , paddle (6 guns, Capt. James Hope) (8 guns, Commander Bartholomew James Sulivan) (18 guns, Commander Edward Augustus Inglefield (acting)) (3 guns, Lieut. Reginald Thomas John Levinge) Fanny, schooner (1 gun, Lieut. Astley Cooper Key) French San Martin (8 guns, Capt. François Thomas Tréhouart) Fulton, paddle (2 guns, Lieut. Louis Mazères (fr)) Expéditive (16 guns, Lieut. Miniac) Pandour (10 guns, Lieut. Duparc) Procida (4 guns, Lieut. de La Rivière) These ships were among the most advanced military machinery of their time, and at least three — Fulton, and — were steamers, which initially stayed behind the sailing vessels. They were partially armoured, and had rapid-fire guns and Congreve rockets. The main Argentine redoubt was located on a cliff rising between 30 and 180 m over the banks at Vuelta de Obligado, where the river is 700 metres wide and a turn makes navigation difficult. The Argentine general Lucio N. Mansilla, commander of the Confederation forces and Rosas' brother-in-law, set up three thick metal chains suspended from 24 boats completely across the river, to prevent the advance of the allied fleet. This operation was under the charge of an Italian immigrant named Filipo Aliberti. Only three of these boats were naval vessels; the rest were requisitioned barges whose owners received a compensation in case of loss. Aliberti was the master of one of the boats, the Jacoba, sunk in the battle. At least 20 boats and barges were lost in the chain barrage at Obligado. On the right shore of the river the Argentines mounted four batteries with 30 cannons, many of them bronze 8, 10, 12 and 20-pounders. These were served by a division of 160 gaucho soldiers. There were also 2,000 men in trenches under the command of Colonel Ramón Rodríguez (es), together with the brigantine Republicano (es) and two small gunboats, Restaurador and Lagos, with the mission of guarding the chains across the river. Some sources increase the Argentine naval power to a third gunboat, the unarmed brigantine Vigilante, whose artillery had been dismounted and transferred to one of the batteries, eight armed launches and at least five armed barges. Main action The combat began at dawn, with intense cannon fire and rocket discharges over the Argentine batteries, which had less accurate and slower loading cannons. From the beginning the Argentines suffered many casualties —