strength to his own forces, the Argentine commander, William Brown, acted rapidly to organize a squadron to advance past the mouth of the Uruguay River, then find and destroy the Third Division. Simultaneously, to stop reinforcements from arriving from the Mariath Division and to secure his rear, he moved to fortify the island of Martin Garcia (called the "Fortress of the Constitution") while he left the defense of the Buenos Aires coast to his flagship, the brig Independencia, along with the brig Republica, the barque Congreso, and four gunboats under the command of Leonardo Rosales. Typical of Brown's audacity, the force he dispatched was in the best case only the equal of the Third Division, while the defense of Buenos Aires was clearly imperiled. The Argentine squadron sailed on 26 December 1826, arriving on the Uruguay River on 28 December. After finding the Third Division, the squadron chased it, catching it in the Yanguari the next day. Brown sent John Halstead Coe, captain of Sarandí to the Brazilian commander as an emissary to request the Brazilians to surrender. Sena Pereira responded by taking Coe prisoner and joining the battle, which lasted until 30 December. However, due to the lack of wind and the narrowness of the channel maneuvering was difficult and the fighting was inconclusive. Unable from gaining access to the narrow channel, Brown withdrew to the south towards Punta Gorda to await the Brazilians. He landed a small force on the Vizcaino Island to secure it and sent instructions to the militia of Santo Domingo de Soriano to cut supplies to the Brazilian fleet. In response, the Brazilians withdrew further north to Concepción del Uruguay (then still usually called "Arroyo de la China") where they could secure supplies. Worried about the menace that the Mariath Division posed to his rear, Brown decided to fully return to Buenos Aires in search of reinforcements for Martin Garcia Island. He ordered Rosales to return the Sarandí to Uruguay via the Paraná de las Palmas while he finished the preparations, after which he rejoined the fleet by travelling aboard a small whaler. Preparations On 6 January the fortification work was begun. The Mariath Division launched an advance on the island with the corvette Maceió and nine other gunships. On 18 January Brown twice ordered his forces out to meet the Brazilian squadron and both times the Brazilians withdrew after an exchange of cannon