Rous entered the Navy on 28 January 1808 (aged just 13) as first-class volunteer on board the , under the command of Captain the Honourable Courtenay Boyle, and the flagship of Sir George Montagu, the Commander-in-Chief, Portsmouth. In February 1809 he moved into the 74-gun , Captain the Hon. Arthur Kaye Legge. After taking part in the Walcheren Campaign, in November 1809 he became a midshipman aboard , flagship of Sir James Saumarez in the Baltic. In March 1811 he joined the ship , Captain John Gore, employed off Lisbon and in the Channel; and from December 1811 he served in the frigate , Captain William Hoste, taking part in the Adriatic campaign.