For several years in the late 1980s I
worked on a national holiday remembering the internment of Japanese
Americans. At the time, I believed that only one person had been a
spy, Hagiwara Makoto, a Japanese national who created and ran the Tea Garden in San Francisco's
Golden Gate Park. He had a short wave radio transmitter in his
office in the tea garden. When the publicity hit, his American
daughter committed suicide at the entrance to the Tea Garden.
I was wrong. Hagiwara-sama was not the only Japanese spy. Michelle Malkin (her blog) in a recent book gives the translation of code MAGIC deciphering of Japanese cables pre-December 1941. On pages 192-196 it is clear that useful military information was being transmitted by a number of spies on the West Coast. MAGIC was declassified in 1977.