Henry was educated at George Watson's Boys' College and Blair Lodge before he enrolled on the training ship HMS "Britannia" at the age of fourteen, in 1890. Rapidly rising in the navy due to keen intelligence and impressive strength, Ritchie was promoted to lieutenant six years later, and served for the next fifteen years as a junior staff officer at Sheerness Gunnery School. In 1900 Ritchie became the armed forces lightweight boxing champion, and was the runner-up in the same contest the following year. In July 1902 he was posted to the battleship HMS "Sans Pareil", docked in the Medway as part of the Reserve squadron.