 Riou entered the navy at 12 years of age, and after a period spent in British and North American waters, served as a midshipman on Captain James Cook's third and final voyage of discovery. Rising through the ranks, he saw service on a number of the navy's stations, but also endured periods of unemployment. He received his first command in 1789, the former frigate HMS Guardian, which was being used to transport stores and convicts to Australia. He had the misfortune to run his ship onto an iceberg, which nearly caused his ship to sink outright. After several attempts to stop the flooding into the damaged hull, most of the crew abandoned ship. Despite fully anticipating his death, Riou refused to leave his ship, and he and a few others were left to attempt the nearly impossible task of navigating the sinking ship several hundred leagues to land. After nine weeks at sea, and with continued labour and endurance, Riou successfully navigated his half-sunk ship back to port, saving the lives of those who had elected to remain with him.
