Is the US Merchant Marine a "US service"? They are (or have been) during wartime, attaching to the US Navy: During World War II the fleet was in effect nation

Is the US Merchant Marine a "US service"? They are (or have been) during wartime, attaching to the US Navy: During World War II the fleet was in effect nationalized; that is, the federal government controlled the cargo and the destinations, contracted with private companies to operate the ships, and put guns and Navy personnel, the Navy Armed Guard, on board. U.S. Department of Transportation Maritime Administration FAQ <https://web.archive.org/web/20150411091000/http://www.marad.dot.gov/about_us_landing_page/marad_faq/FAQ.htm#q1 https://web.archive.org/web/20150411091000/http://www.marad....>