Battle of Riachuelo

Paraguay was a landlocked country whose only route to the world ran down the Parana and the Paraguay rivers, so when Solano Lopez went to war with his three larger neighbours the rivers were the war. On 11 June 1865 his flotilla, converted merchant steamers with guns bolted on, came down on the Brazilian squadron at anchor, planning to board. Engine trouble delayed the attack past dawn, the Brazilians got steam up, and what was meant to be an ambush became a nine hour running fight that Barroso finished by ramming. Four Paraguayan ships were destroyed and the rest driven upriver. From that day Paraguay was sealed in, and the war became a five year siege of a whole country.

The War of the Triple Alliance killed a larger share of one country's population than any other war in modern history by most reckonings, and the Paraguayan death toll is the most disputed number in South American historiography, with credible estimates ranging from under a fifth to nearly seven in ten of the pre-war population. Interpretation swings with politics: nineteenth century Brazilian and Argentine accounts cast Lopez as a tyrant, twentieth century revisionists recast him as an anti-imperialist martyr, and the Lopezista reading is still official in Paraguay. Riachuelo's role is the one point of broad agreement, since sealing the rivers is what converted a war of manoeuvre into a war of attrition Paraguay could not survive. The battle is commemorated on both sides of the river, and several of the wrecks are thought to remain in the Parana channel.