According to the DVD sleeve notes, prior to production James Cagney trained intensively in the martial art of judo in preparation for his role. He trained under Ken Kuniyuki, who was a 5th Degree Judo Master. Cagney insisted that he perform his own stunts. He said in his memoirs, "I grew so fond of judo I used it to keep in shape until a back injury I picked up doing something else put me on the sidelines." Moreover, another instructor for Cagney was former LAPD policeman John Halloran, who plays the role of Capt. Oshima and can be seen in the closing fight sequence. Apparently Halloran quit the LAPD after FBI agents investigated him because he was an expert in judo.
The movie is based on the history behind Japan's alleged Tanaka Plan, aka the Tanaka Memorial document (it was made public after his death in 1929). This allegedly was Prime Minister Baron Gi-ichi Tanaka's militarist strategic plan for world domination prepared for Emperor Hirohito. It was first printed in China by the Chinese communists and in the US by a communist periodical, leading some to think that it was a forgery. No Japanese version has ever been found.
The Tokyo Imperial Hotel bar seen at the start of the movie is apparently an exact replica of the bar situated in the Imperial Hotel in Tokyo which was designed by Frank Lloyd Wright.
The DVD sleeve notes claim that this was one of the first American martial arts movies. Though not a martial arts movie by modern standards and definitions, judo is seen in the movie and with James Cagney performing it. Cagney insisted on doing his own stunts in the film.