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At the beginning, the Japanese soldiers, who are trained by the Americans, are using American-made Model 1861 Springfield muskets and British-made Pattern 1853 Enfield muskets, no doubt surplus from the American Civil War (which ended eleven years before the beginning of the movie). At the final battle, however, the now better trained and better equipped army can be seen using Prussian-made Gewehr 1871 bolt-action Mausers, a single-shot, bolt-action, black-powder cartridge rifle. This rifle, unlike modern bolt-action rifles, had no magazine (the Model 1871/84 would add a tubular magazine). This equipment update is also reflected in the dress of the Japanese soldiers, which abandoned the American 1870s look of the first part of the movie and adopted a stern, militaristic Prussian look (dark blue blouse, white gaiters, the more military style cap of a professional army instead of a French-style kepi then used by the U.S. Army). This is because the elite Japanese units during this time were trained by Prussia, and the Model 1871 Mauser was widely exported during the 1870s-1880s and was not fully replaced even in Prussian/German service until 1889.
Tom Cruise spent almost two years in preparation for this movie, including swordplay instruction and Japanese-language lessons.
This not only marks the first time Ken Watanabe starred in an American-made movie, but it is the first time he spoke English in a movie.
The swordsmith in the village is a real swordsmith. His name is Shoji Yoshihara, brother to Yoshihara Yoshindo. Shoji is a "Mukansa"-level master swordsmith, one of the highest rankings in Japan.
Contrary to popular misconception, the title of this movie does not refer to Captain Nathan Algren or Katsumoto. The word "Samurai" here is in its plural form, and referrs to Katsumoto's clan as a whole.
Although this movie seems to imply that Japan's new army was trained by the Americans, in fact, it was the Prussian General Staff that assisted in the modernization of Japan's army.