About US Military Branches...
The President of the United States is the commander in chief of the entire United States military. This is a huge power as the US military is one of the most powerful in the world.
The US Army is mainly responsible for most infantry and ground vehicle combat.
The US Navy is mainly responsible for boats and other elements of naval (sea) combat.
The US Marine Core is an all-around group that uses ground vehicles, aircraft, and all kinds of weaponry.
The US Coast Guard is responsible for protecting the coasts of the US usually by boats.
The US Air Force is mainly responsible for aircraft warfare.