Military organization specialized in amphibious warfare
Marines (or naval infantry) are military personnel who primarily operate in littoral zones, both on land and at sea. Historically, the main tasks undertaken by marines have included raiding ashore in support of naval objectives, and the boarding of vessels during combat or capture of prize ships. Marines also help maintain discipline and order aboard the ship (reflecting the pressed nature of the ship's company and the risk of mutiny).
https://en.wikipedia.org/wiki/Marines