Upon the outbreak of war with Spain in 1898, the twin-screw protected cruiser was quickly readied for service, with Glass in command. Commissioned on 5 May 1898, "Charleston" set out for the Hawaiian Islands 16 days later. Escorting three transports—"City of Peking", "Australia", and "City of Sydney"—she sailed from Honolulu on 4 June, bound for Manila, Philippines. When clear of land, Glass opened his confidential orders, which directed him to take the island of Guam while en route to the Philippines. Her mission thus outlined, "Charleston" altered course for Guam, and the cruiser and her three consorts reached their interim destination at daybreak on 20 June. Leaving the transports anchored outside, "Charleston" boldly entered the harbor and fired a challenge, only to receive no return fire of any kind. Spanish emissaries soon called upon Glass and were astonished to learn that a state of war existed between their respective countries. As the island was virtually undefended—the forts were in ruins—the Spanish governor surrendered; and Glass took possession of Guam for the United States on the afternoon of 21 June 1898.