By early 1814, Montevideo remained a major royalist stronghold because Spanish ships could still resupply it by sea. Buenos Aires responded by fitting out a small fleet and putting Guillermo (William) Brown in command, making naval control of the Río de la Plata a central part of the independence struggle.
Brown’s fleet fought for control of Martín García Island, a strategic point near the mouths of the Paraná and Uruguay rivers. The United Provinces’ victory helped open river routes and weakened the royalist naval position around Montevideo.
A small patriot division attacked royalist vessels near Arroyo de la China (near today’s Concepción del Uruguay) but was repulsed. Although tactically costly, the action did not reverse the wider campaign, which depended on cutting Montevideo’s sea supply lines.
After gaining key positions, Brown moved to seal Montevideo from the sea while patriot forces maintained pressure on land. The blockade aimed to stop food, ammunition, and reinforcements from reaching the royalist garrison, turning naval power into a direct tool of siege warfare.
Royalist ships sailed out from Montevideo to force a passage through the patriot cordon. This move led directly to a multi-day battle off the coast near Buceo, where Brown sought to finish control of the estuary.
Between May 14 and May 17, 1814, Brown’s squadron defeated the Spanish fleet off Montevideo. The result left Montevideo effectively cut off by sea, creating the conditions for the city’s surrender and marking a turning point in the Río de la Plata naval war.
With sea supply routes shut down and land forces maintaining the siege, Montevideo’s royalist leadership faced worsening shortages. The city capitulated weeks after the naval defeat, ending the main Spanish naval base in the estuary and shifting momentum to the revolutionary side.
After the 1814 campaign, Buenos Aires expanded maritime pressure by encouraging corso (privateering), issuing commissions for privately armed ships to capture enemy commerce. This strategy aimed to weaken Spanish logistics and finance beyond the Río de la Plata, especially as the war spread across South America.
In September 1815, Brown departed Buenos Aires on the Hércules as part of a long-distance privateering effort aimed at Spanish trade and naval power on the Pacific coast. The voyage around Cape Horn signaled that the Río de la Plata conflict could project force far beyond local waters.
In January 1816, Brown reached El Callao, the fortified port serving Lima, and began attacks designed to disrupt Spain’s main Pacific naval base in the region. Even without capturing the fortress, the operation demonstrated how privateering could threaten Spanish communications and commerce at a strategic hub.
In early February 1816, Brown attacked defenses near Guayaquil but became trapped and was captured during the fighting. He was later freed through negotiation and prisoner exchange, highlighting both the reach and the risks of these distant naval operations.
After months at sea, Brown reached the Caribbean, where the British sloop HMS Brazen captured the Hércules at Barbados in September 1816. The seizure reflected the legal and diplomatic tension between British neutrality and revolutionary privateering in Spanish waters.
Following the capture, Brown pursued legal appeals over the Hércules and its cargo, a process that stretched across multiple proceedings. The drawn-out case shows how naval warfare and privateering were closely tied to international law and great-power politics.
By 1818, Brown had returned to Buenos Aires after years of combat and legal battles linked to his Pacific privateering cruise. His 1814 victory at Buceo had helped bring down Montevideo, and his later operations extended the war at sea—leaving a lasting model for how the revolutionary state could use naval power, blockade, and privateering to shape the independence struggle.
Naval warfare in the Río de la Plata and Guillermo Brown's operations (1814–1819)