I didn't know Americans were stripped of their citizenship, that is quite a sacrifice to make and dbaggery on the part of the USA government.
This raised my eyebrows also so I looked into it. I have a biography titled
"Spitfires, Thunderbolts and Warm Beer" which is about an American who joined the RAF before Pearl Harbor. LeRoy Gover was recruited and trained at an RAF-contracted flying school in Bakersfield, California. In the book, when Gover graduates and is ready to 'ship out,' the author explains:
Preparation for the trip included more than packing clothes in a small bag and saying good-bye to friends and loved ones. What Gover and the other graduates of the several Clayton Knight-sponsored flying schools in the United States were doing was technically illegal. In a desperate effort to stay out of the war in Europe, the United States had passed a Neutrality Act almost annually from 1936 through 1941. Two provisions of these acts were especially significant to Lee and his compatriots. The first specified that service in the armed forces of a foreign power without authorization and with the resultant acquisition of foreign nationality would expatriate an individual. In other words, they could lose their American citizenship. Fortunately for Gover and the hundreds of other young men who joined the Royal Air Force, the State Department made the decision in June 1940 that so long as a person did not swear allegiance to another government, he would not lose his citizenship. The other provision provided that travel through a designated war zone (the North Atlantic) or on board a belligerent ship (British) could result in a prison sentence of up to two years and/or a $10,000 fine. Fortunately for everyone involved, there was never any prosecutions under this law. Apparently the danger in traveling across the submarine-infested North Atlantic was punishment enough.
In addition, it was illegal for any person registered with Selective Service to leave his home area without telling his draft board where he was going. Travel to Canada was particularly suspect, because most draft boards knew that many Americans, especially pilots, were going to Canada as a first step in eventually gettin to England. When Gover made his decision to sign up for the RAF, he talked to his girlfriend's father, the president of the San Carlos draft board, about what he intended to do. The result was a "Permit of Local Boart for Registrant to Depart from the United States," which gave Gover permission to go to Canada on a business trip for sixty days. Although a provision of the permit stated that "the granting of such permit will not result in evasion of or interference with the execution of the Selective Service Law," the board knew that Gover was going to Canada and then to England to be a member of the RAF, so was clearly was making it impossible to draft him.
Gover: "I think one reason the draft board let me go was the long talks that I had with the board president about the prospect of war and my inability to get into U.S. pilot training because I lacked the required two years of college. I used to take his daughter to San Francisco on dates, and we would sit and watch the Japanese ships loaded to capacity with scrap metal sailing through the Golden Gate for Japan. I really believed that someday that metal would be used against us just as it was then being used against China. He agreed with my thoughts and understood well why I wanted so badly to fly. Once I got the permit, the rest was easy. I crossed the border with no trouble and never heard anything about it."
