Navies are military forces that operate at sea, primarily responsible for protecting a nation's interests on the water. They consist of various ships, submarines, and aircraft, which work together to ensure maritime security, conduct naval warfare, and support humanitarian missions. Navies play a crucial role in international relations and can project power beyond a country's borders. Navies are often organized into fleets, which may include different types of vessels such as aircraft carriers, destroyers, and submarines. Each type of ship has specific functions, from launching air strikes to conducting underwater operations. Countries with significant naval capabilities include the United States, China, and Russia.