It's set at the time of Commodore Matthew C. Perry's second trip to Japan, in February 1854, and his attempt to get a signed treaty with the Shogun. The basic plot borrows more than a little from the 1972 samurai western, RED SUN, and has to do with the theft of a sword intended for the U.S. president by a Japanese faction opposed to the treaty. Acting without orders, three Americans--a marine captain and two sailors, one of whom speaks a little Japanese--go off in pursuit of the sword and have numerous encounters in the Japanese countryside before the big confrontation at the castle of Lord Yamato, the nobleman behind the theft of the blade.
Quite improbably, the Americans encounter more than a few Japanese--five in all--who happen to speak adequate English, one of whom, Enjiro (played by Japanese-American actor Mako), is based on an actual historical figure, the fisherman Manjiro, who had been shipwrecked and taken to America some years earlier, but who actually had no interaction with the Americans during Perry's second trip. The other Japanese characters are all rather unlikely candidates to be proficient English speakers in 1854 Japan, but they include some big name actors. Toshiro Mifune (YOJIMBO) plays the Shogun's Commander; Sonny Chiba (THE STREET FIGHTER) plays Prince Ido, a foe of Yamato; and Tetsuro Tamba (YOU ONLY LIVE TWICE) plays Lord Yamato. Laura Gemser seems to have wandered in from Italian exploitation films (the EMANUELLE series) to play a half-Japanese, half-'foreign' English-speaking female samurai who beds the American captain.
The only big names in the American cast are Richard Boone, a one-time TV star ('Have Gun, Will Travel') and character actor in his final film role (as Commodore Perry), and James Earl Jones, who has a cameo as a shipwrecked sailor who's been held by the Japanese for two years. The biggest American part, Captain Hawk, is played by Frank Converse, primarily a TV actor ('NYPD'), who is actually quite good at portraying America's particular 19th century brand of arrogance and self-importance. Timothy Murphy plays the young American lieutenant who becomes enamored of Japanese culture (and falls for a Japanese woman). Mike Starr, later a prominent character actor and comic player (GOODFELLAS, ED WOOD, DUMB AND DUMBER), appears in his first film as burly sailor Cave Johnson, who takes on a sumo wrestler in one of the film's comic sidebars.
Overall, the film is of interest to Japan buffs and samurai fans, but it's bound to be a disappointment to most others because of its hackneyed story, stilted direction and TV-movie style of shooting. The film got very little theatrical release in the U.S. and went straight to television in most areas.