Actually, the U.S. could flag it (if we had the nads..). The Privateering acts have never been rescinded- they're still valid, and active..just they havent been issued in a while..
No letter of marque has been legitimately issued by the United States since the nineteenth century. The status of submarine hunting Goodyear airships in the early days of the second world war has created significant confusion. According to one story, the United States Navy issued a Letter of Marque to the Airship Resolute on the West Coast of the United States at the beginning of World War II, making it the first time the US Navy commissioned a privateer since the War of 1812.[14] This story, along with various other accounts referring to the airships Resolute and Volunteer as operating under a "privateer status", is highly dubious. Since neither the Congress nor did the President appear to have authorized a privateer during the war, the Navy would not have had the authority to do so by itself.[15]