William Stewart's next appointment was as lieutenant in the 50-gun razee frigate "Grampus", which was commissioned at Woolwich by Captain Henry Byam Martin, and then went out to the Pacific station. Stewart served in "Grampus" until 1847, when he studied steam engineering at Woolwich. On 18 May 1848, he was promoted to commander. On 5 August 1851, Commander Stewart commissioned the 6-gun paddle-sloop "Virago" at Woolwich. "Virago" served on the Pacific station. On 4 December 1851, "Virago" put into the Chilean port of Punta Arenas in the Strait of Magellan. This city was "a penitentiary colony for relapsing criminals and relegated military". When "Virago" arrived, the port was in the hands of a group of mutinous prisoners "headed by one Cambiaso, second lieutenant of the troops stationed there; who... had committed some offence and been imprisoned a short time before." Cambiaso had captured two merchant vessels: the barque "Florida" of New Orleans and the brig "Eliza Cornish" of Liverpool. The officers of the "Virago" came on shore, visited the barracks, and the "Florida", and then left the harbour without having their suspicions excited. When "Virago" arrived Cambiaso had considered trying to capture her, but was deterred because of "the order and discipline on board, the well manned guns, the well drilled marines", and "of the capability of even the smallest midshipman to take command of the crew in case of the absence of the superior officers". Early in January 1852, intelligence of the mutiny was transmitted to the Chilean government at Valparaíso. "The Chilean authorities despatched two Chilean men-of-war ["Indefatigable" and "Meteoro"], and some Chilean troops under Don Santiago Jorge Bynon. The troops were put on board the Chilean men-of-war; the latter on board the "Virago", on the same service. The English steamer proceeded immediately to the Straits, and it was to be hoped that her officers would learn a lesson from experience, and prove themselves more sharp sighted than they had done a month before, in their former visit to the colony." The mutineers and their prisoners sailed from Punta Arenas on the "Florida" and the "Eliza Cornish".