The Royal Marines' motto is Per Mare Per Terram; By Sea By Land. It is not known when this motto was adopted, but it first appeared on the caps worn by the Marines at the battle of Bunker Hill in 1775.
It is of interest that the plural of this motto Per Mare Per Terras is one of the mottoes of the MacDonalds. The son of the Jacobite heroine, Flora MacDonald, served with the Marines in the American War of Independance.