What is the difference between Armed Forces Day and Veterans Day? The United States will celebrate Armed Forces Day on 15 May, which is held to honor all serving personnel across the six branches of the US military. Tim Nwachukwu AFP The United States will mark Armed Forces Day on 15 May, one of the three main national events to honor all current serving US military personnel across the six branches of the military within the US Department of Defense: the US Army, US Navy, US Marine Corps, US Air Force, the US Coast Guard and the recently created US Space Force.