The act only specifically applies to the United States Army and, as amended in 1956, the United States Air Force. While the act does not explicitly mention the United States Navy and the United States Marine Corps, the Department of the Navy has prescribed regulations that are generally construed to give the act force with respect to those services as well. The act does not apply to the Army National Guard or the Air National Guard under state authority from acting in a law enforcement capacity within its home state or in an adjacent state if invited by that state's governor. The United States Coast Guard, which operates under the Department of Homeland Security, is not covered by the Posse Comitatus Act either, primarily because although the Coast Guard is an armed service, it also has both a maritime law enforcement mission and a federal regulatory agency mission.

Can we conclude that can the national guard be used for law enforcement?
yes