It was the first naval engagement between both navies and took place in front of Huanillos, off the (then) Bolivian coast, as the Peruvian corvette Unión and gunboat Pilcomayo found the Chilean corvette Magallanes on its way to Iquique.

For a while, the Unión was subjected to cross fire, then the Pilcomayo suffered boiler trouble, and dropped out of the battle.

After a two-hour running artillery duel, Unión suffered engine problems, the pursuit was called off.

Magallanes escaped with minor damage and had completed part of its mission, delivering commissioned papers to Iquique, but could not complete its reconnaissance mission of finding if any guano ships were still trading in the zone.

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