Much of the film recounts actual historical events, including Shingen's death and the two-year secret, and the climactic Battle of Nagashino in 1575. Those scenes are also modeled closely on detailed accounts of the battle.
The battle scenes utilized hundreds of horses and thousands of extras. According to George Lucas, the picture had five thousand extras in the film's battle sequence finale which depicted the Battle of Nagashino of the year 1575.
When Toho Studios couldn't fulfill the budget demands of the film, American film directors George Lucas and Francis Ford Coppola stepped in to help Akira Kurosawa. Kurosawa was visiting San Francisco in July 1978 and met Lucas and Coppola. The two convinced studio 20th Century-Fox, still riding high after the success of Lucas' La Guerre des étoiles (1977), to advance-finance the film and fund the remaining portion of the budget. This was done in exchange for the film's world-wide distribution rights to the picture outside of Japan. This was the first time that distribution rights to a Japanese film had been pre-sold to a major Hollywood studio.
Final feature film of actor Takashi Shimura. He was one of director Akira Kurosawa's favorite actors, and Kurosawa used him regularly. This movie was their final collaboration. Kurosawa wrote the part of Gyobu Taguchi in this film for him. The scene in which Shimura appears was cut from the international subtitled version of the film but has been put back in the modern subtitled DVD release. Shimura passed away in 1982.
After Kurosawa fired Shintarô Katsu from the leading double role, the American producers requested that a internationally known star be cast instead. Because Kurosawa had distanced himself from Toshirô Mifune more than a decade earlier, Tatsuya Nakadai was his only viable option. Mindful of the situation Nakadai accepted the part without even reading the script. He later admitted that the decision was not easy because he had been on friendly terms with Katsu. Purportedly Katsu did not speak to Nakadai for several years after the whole incident.
Akira Kurosawa: [weather] There's a rainy scene just before the final battle of the film, not to mention the rainbow part which is one of the most memorable parts of the film.