Assigned to the Pacific Squadron, "Mohongo" departed Brooklyn on 29 May 1865 for the west coast of South America. Sailing via St. Thomas, Barbados, Natal, Rio de Janeiro, and Montevideo, making official protocol visits to those Caribbean and Latin American ports, the "double‑ender" steamed through the Strait of Magellan in a severe gale on 9 October and arrived at Valparaíso, Chile, on the 29th. She remained there repairing her storm-damaged pumps and boilers until standing out on 27 April 1866 for Callao, Peru. Arriving six days later, the warship joined Rear Adm. George F. Pearson's Pacific Squadron in the midst of a Spanish blockade during the Peruvian War with Spain over conditions of the treaty recognizing Peru's independence. "Mohongo" remained at Callao with the rest of the squadron, protecting American lives and property from attack by either side until departing on 21 May for a month's cruise up the coast of South America to Guayaquil, Ecuador, on a protocol visit.