<P> Naval infantry, commonly known as marines, are a category of infantry that form part of a state's naval forces and perform roles on land and at sea, including amphibious operations, as well as other, naval roles . They also perform other tasks, including land warfare, separate from naval operations . </P> <P> During the era of the Roman empire, naval forces included marine legionaries for maritime boarding actions . These were troops primarily trained in land warfare, and did not need to be skilled at handling a ship . Much later during the age of sail, a component of marines served a similar role, being ship - borne soldiers who were used either during boarding actions, as sharp - shooters, or in raids along shorelines . </P> <P> The Spanish Infantería de Marina was formed in 1537, making it the oldest, current marine force in the world . The British Royal Marines combine being both a ship - based force and also being specially trained in commando - style operations and tactics, operating in some cases separately from the rest of the Royal Navy . The Royal Marines also have their own special forces unit . </P> <P> In the majority of countries, the marine force is an integral part of the navy . The United States Marine Corps is a separate armed service within the United States Department of the Navy, with its own leadership structure . </P>

Who has the oldest navy in the world