Marines, also known as naval infantry, are typically an infantry force that specializes in the support of naval and army operations at sea and on land and air, as well as the execution of their own operations. In many countries, the marines are an integral part of that state's navy. In others, it is a separate organization altogether, such as in the United States, where the Marine Corps falls under the US Department of the Navy, yet it operates independently (and similarly the UK's Royal Marines come under Her Majesty's Naval Service). Marines can also fall under a country's army like the Troupes de marine.
Historically, tasks undertaken by marines have included: helping maintain discipline and order aboard the ship (reflecting the pressed nature of the ships' company and the risk of mutiny), the boarding of vessels during combat or capture of prize ships, and providing manpower for raiding ashore in support of the naval objectives.
With the industrialization of warfare in the 20th century the scale of landing operations increased. This brought with it an increased likelihood of opposition and a need for co-ordination of various military elements. Marine forces evolved to specialize in the skills and capabilities required for amphibious warfare.