The War of the Pacific began in April 1879 over control of the Atacama Desert's saltpeter deposits, a mineral wealth that had made the arid borderlands between Chile, Bolivia, and Peru some of the most economically contested territory on the continent. Bolivia lost not only its mining regions but its entire coastline. Peru stood to lose the southern province of Tarapaca. After Chile seized naval supremacy at the Battle of Angamos on October 8, 1879, the question was no longer whether a land invasion would come, but where. Chilean War Minister Rafael Sotomayor chose Pisagua, a small port 500 kilometers north of Antofagasta, planning the operation in secrecy so strict that not even his own military commanders knew the target until the fleet was at sea. By October 19, a convoy of six warships and nine transports carried 9,405 soldiers and 853 horses and mules toward the Peruvian coast.

Pisagua's defenders had geography on their side. A narrow bay flanked by two fortified positions, each armed with a 100-pounder cannon, created a crossfire that could rake any ship attempting to enter the harbor. Steep hillsides rose directly behind the beach, giving the roughly 1,200 Bolivian and Peruvian defenders the high ground. At 7:00 in the morning, the Chilean warships Cochrane and O'Higgins entered the bay and opened fire on the southern fort at Pichalo Point. The Magallanes and Covadonga attacked the northern position. The gunships' fire was devastatingly accurate. The northern fort managed a single shot before being temporarily disabled. Within an hour, both forts were silent. But when the landing was delayed and the northern cannon resumed firing, the Cochrane answered immediately, and by 9:00 the bay was open.

At 10:15, the navy ceased its barrage and the first boats pushed toward shore. The 450 soldiers who landed belonged to the Atacama Battalion and the Zapadores Regiment. They came under immediate fire from the heights above Playa Blanca, where Bolivian troops poured rounds down on the exposed beach. The situation was desperate. Ricardo Santa Cruz led the Zapadores in a direct assault up the hillside, fighting for every meter of slope against entrenched defenders firing from above. Meanwhile, the Allied troops had taken cover behind bags of saltpeter and coal, which caught fire during the exchange. The thick, acrid smoke drifted across the landing zone and inadvertently screened the arrival of the Chilean third wave. As the Bolivian defenders began retreating toward the train station at Alto Hospicio, the main assault on the plateau began. It took two hours of brutal climbing under fire for Chilean infantry to reach the summit, where hand-to-hand fighting finally broke the Allied line. Lieutenant Rafael Torreblanca raised the Chilean flag over Alto Hospicio at 3:00 in the afternoon.

Chile lost 56 dead and 124 wounded. The Bolivian-Peruvian alliance suffered roughly 200 casualties. The numbers were modest, but the strategic result was decisive. Pisagua gave Chile a functioning port through which to land the troops, weapons, and supplies needed for the Tarapaca Campaign. The province's saltpeter wealth, the very prize over which three nations had gone to war, was now within reach of Chilean forces pushing inland. The territory changed hands permanently. The Treaty of Ancon in 1884 annexed Tarapaca to Chile, and Bolivia lost its Pacific coastline forever, a grievance that persists to this day. The Chilean Army and Marine Corps still celebrate November 2 as a military holiday. What began as a messy, undersized landing against fortified cliffs became, in retrospect, the opening act of a campaign that redrew the map of South America.