A more thorough explanation:

The United States Navy is a branch of the United States armed forces that is responsible for naval operations. This includes naval aviation and the United States Marine Corps, as well as the United States Coast Guard when it is operating as a service in the Navy. The Navy is under the authority of the U.S. Department of the Navy and is abbreviated as USN.

For example, the United States Navy is responsible for protecting the country's coastlines and conducting military operations at sea. They use ships, submarines, and aircraft to carry out their missions. The Navy also provides humanitarian aid and disaster relief around the world.

Another example is the Navy's role in supporting national security. They work closely with other branches of the military and intelligence agencies to gather information and respond to threats to the United States.