When you join the Armed Forces of the United States of America, you enter into a contract with the U.S. Government. Each of the five branches is different and has different missions and functions that are primary. Knowing the responsibilities of each one can help you choose what is the best fit for you.
Army- The U.S. Army is the military service that is the oldest, having been established in June of 1775. It is also the biggest, with nearly a half million enlisted and Officers. The ground-force for the United States is primarily the U.S. Army. The Army has as its main function the job of defense and protection of the United States and our interests. Army aircraft, artillery, armor, and ground troops take care of this mission quite well. The National Guard, when activated, is part of the US Army.
Air Force- Just as the US Army is the oldest; the Air Force is the youngest of the five services. It took shape just after World War II, in 1947. Its primary purpose and mission is to use Air and Space to defend and protect our interests and the United States at large from all enemies, foreign and domestic. About three hundred fifty thousand Service members serve in the Air Force.
Navy – The Navy is almost as old at the Army, established just a few months after the Army in 1775. Its primary mission is to insure the freedom of the seas for the United States and its allies, and freedom loving people worldwide. Navy Air power also supplements the Air Force, using ground based and Aircraft carrier based aircraft of all shapes and sizes. The Navy also has ships and submarines, all used to provide and protect the United States. The Navy is also responsible to transport Marines where they are needed.
Marine Corps. The Marines were established also as part of the Navy in 1775. They are the ground forces that are charged with taking the beach, securing an area. They are specialized and experts in ground warfare.
Coast Guard –Originally called the Revenue Cutter Service, and established in 1790, the U.S Coast Guard was recently transferred to the Department of Homeland Security. Their primary mission is Search and Rescue, followed by Coastal Law Enforcement, and Illegal Immigration.
So, knowing a little bit about each service can help make you informed, and allow you to chose the service that you want to be an enlisted member of.