Um, the entire Armed forces of the United States are under the command of the President. He being the Commander and Chief an all. He's the very top of the chain of command.

But, congress also controls what the Army, Navy, Airforce, and Coastguard does too.

The President is the Commander in Chief and the boss of all the military. The United States Coast Guard actually reports to the Department of Transportation, although during war they are "activated" under DoD. The United States Congress has a "veto" over the use of the armed forces through the War Powers Act that was passed in the wake of Vietnam. I am very rusty on all its provisions, but it eventually means that for the Commander in Chief (President) to deploy forces for more than 60 days (maybe 90, I can't remember exactly), Congress must authorize it. Hence, the reason that Bush 41 and Bush 43 got resolutions from Congress authorizing the use of military force against Iraq and Iraq. A side benefit is that the support of Congress helps to sway public opinion in favor of the action, as well. Another way in that Congress has strong oversight is through the budgetary process. However, it is definitely the President who calls the shots based on the advice of the civilian and military leadership at the Pentagon.

Prior to the War Powers act, only the Marine Corps could be deployed without an congressional approval. Now all services can. The MC is the only service tasked to perform such duties as the President may direct under the NSA of 1947.

Thanks for clearing that up for me Sam.