The United States Navy Sea, Air and Land (SEAL) Teams, commonly known as Navy SEALs, are the U.S. Navy's principal special operations force and is a part of the Naval Special Warfare Command (NSWC) as well as the maritime component of the United States Special Operations Command (USSOCOM). The SEAL name is derived from their capacity to operate at sea, in the air and on land, but it is their ability to work underwater that separates SEALs from most other military units in the world. The experience gained from operating in the ocean and fresh water battle fields has shaped their identity and, as a result, they are regarded as being amongst the most highly skilled and trained amphibious units in the world[citation needed]. Navy SEALs are trained and have been deployed in a wide variety of missions, including direct action and special reconnaissance（侦查） operations, unconventional warfare(非常规战), foreign internal defense（协防）, hostage rescue, counter-terrorism, and other missions.Without exception, all SEALs are male members of either the U.S. Navy or the Coast Guard.