The name Nanawa comes from Enxet, the language of an Indigenous people of the Chaco, and means "carob tree forest." The Paraguayans had established the outpost in 1928, and by the end of 1932 it had become their strongest position on the southern front. The Chaco itself made every fortification a gamble. This is flat, thorny, drought-stricken country where water is scarce and the heat punishing, and where an army's true enemy is often the land rather than the man across the wire. Disease and thirst killed as freely as gunfire. Holding Nanawa meant holding a road toward the Paraguayan heartland, and both sides understood what was at stake in the dust. For a country of barely a million people, losing this outpost could mean losing the war.

The Bolivian commander-in-chief was Hans Kundt, a German veteran of the First World War who believed in the massed frontal attack and commanded the assault from the field himself. Against Nanawa he sent his 7th Division, some 3,600 men reorganized into reduced regiments. Facing them stood the roughly 2,500-strong Paraguayan 5th Division under Colonel Luis Irrazábal, who had gathered four regiments and several smaller units behind the horseshoe. From 20 to 26 January 1933, the Bolivians attacked again and again. Three assaults clawed into parts of the stronghold and then stalled, unable to break the line. The cost was heavy, the Bolivian army absorbing some two thousand casualties for ground it could not keep. Many of those men were highland conscripts, sent down from the thin cold air of the Andes into a lowland heat that sapped them before they ever reached the Paraguayan wire.

When the frontal attacks failed, the Bolivians changed tactics, trying to dig a trench all the way around the Nanawa complex and strangle it. Paraguayan reinforcements broke up the effort. Then the weather intervened. Heavy rains turned the Chaco's hard ground to mud and forced the Bolivians to abandon the portions of the complex they had seized, and the Paraguayan garrison soon recovered those positions. Kundt's army did not withdraw far. It dug itself into a semicircle around the Paraguayan trenches and waited, the two sides settling into the close, grinding proximity that would come to define this front. The carob-tree forest had held, but everyone sensed it was not finished. The Bolivians would come back in July, in the dry season, for the Second Battle of Nanawa, and that second attempt would be bloodier still.

Taken together, the two battles of Nanawa became among the bloodiest fought in South America in the twentieth century, earning the grim nickname the "South American Verdun" after the meat-grinder of the First World War. The fighting left its mark on culture as well as the land. A Paraguayan polka, 13 Tuyutí, was inspired by the battle, its lyrics written in Guaraní by the poet Emiliano R. Fernández, who was himself a soldier in the 5th Division and was wounded in the Bolivian assault. The men who held the trenches were conscripts and volunteers from a country of barely a million people, and the songs that remember them are still sung today.