The Royal Marines (RM) are the marines and amphibious infantry of the United Kingdom and, along with the Royal Navy and Royal Fleet Auxiliary, form the Naval Service . They are also the United Kingdom's specialists in mountain and Arctic warfare. A core component of the country's Rapid Deployment Force, the Corps' 3 Commando Brigade is capable of operating independently and is highly trained as a commando force. It can deploy quickly and fight in any terrain in the world.