Got me curious so I Googled it. Looks like there’s been six treason convictions over the past one hundred years. Of those two involved veterans.

Walter Allen was convicted of treason on September 16, 1922 for taking part in the 1921 Miner's March with the coal companies and the US Army on Blair Mountain, West Virginia.

Martin James Monti, United States Army Air Forces pilot, convicted of treason for defecting to the Waffen SS in 1944.

Robert Henry Best, convicted of treason on April 16, 1948 and served a life sentence. He was commissioned in 1918 and stayed in the U.S. Army until 1920.

Iva Toguri D'Aquino, who is frequently identified by the name "Tokyo Rose", convicted 1949. Subsequently, pardoned by President Gerald Ford.

Mildred Gillars, also known as "Axis Sally", convicted of treason on March 8, 1949; served 12 years of a 10- to 30-year prison sentence.

Tomoya Kawakita, sentenced to death for treason in 1952, but eventually released by President John F. Kennedy to be deported to Japan.