In May 1575, Takeda Katsuyori (武田勝頼, Takeda Katsuyori) led approximately 15,000 men into Mikawa Province (三河国, Mikawa-no-kuni) and laid siege to Nagashino Castle (長篠城, Nagashino-jō), held by only 500 Tokugawa troops under desperate conditions. The Takeda were the most formidable cavalry force in Japan — the inheritance of Takeda Shingen (武田信玄, Takeda Shingen), the tactical genius whose horsemen had terrorized central Japan for decades. Katsuyori was fighting to restore his father's prestige and extend his domain. He had no reason to doubt his own army.

Tokugawa Ieyasu (徳川家康, Tokugawa Ieyasu), age 32, called for help. Oda Nobunaga (織田信長, Oda Nobunaga), age 41, responded in person with a large force, bringing the combined Oda-Tokugawa army to approximately 38,000 men. Nobunaga chose his ground carefully. At Shitaragahara (設楽原, Shitaragahara), a field approximately four kilometers west of Nagashino Castle, he constructed a series of wooden palisades across the open terrain. Behind those barriers he positioned approximately 3,000 of his best arquebusiers (鉄砲隊, teppōtai). The key innovation was not simply the number of guns — firearms had been in Japan since Portuguese traders landed on Tanegashima (種子島, Tanegashima) in 1543, just over thirty years earlier. The innovation was the system: Nobunaga organized his gunners into rotating firing ranks, so that one line was always loaded and ready while another discharged. There would be no gap. Cavalry, which derived its battlefield value from speed and the ability to exploit openings in an opponent's firepower, would find no opening here.

Katsuyori reportedly received warnings from several of his most experienced generals, who saw what Nobunaga had prepared and urged caution. He overruled them. The reasons are not clearly documented in contemporary sources — later chronicles supply dramatic motives, but these should be read as traditional narrative. What is documented is that the Takeda cavalry charged, repeatedly, into the killing field Nobunaga had built specifically to receive them.

The palisades had gaps designed for arquebuses to fire through. In front of those gaps ran a stream. The charging horses were forced to slow as they crossed the water — and within roughly 50 meters of the barricades, the rotating volleys cut them down. The Takeda charged again. And again. Each charge met the same result: the guns were always ready.

The battle on approximately June 28, 1575 — some sources give June 29, a one-day difference in converting the Japanese lunisolar calendar — ended with catastrophic Takeda losses. Approximately 10,000 Takeda soldiers died. Of 97 named Takeda commanders, 54 were killed, including eight of the revered Twenty-Four Generals (二十四将, Nijūshi-shō) of Takeda Shingen: Baba Nobuharu (馬場信春, Baba Nobuharu), Hara Masatane (原昌胤, Hara Masatane), Yamagata Masakage (山県昌景, Yamagata Masakage), Naito Masatoyo (内藤昌豊, Naitō Masatoyo), Sanada Nobutsuna (真田信綱, Sanada Nobutsuna), Sanada Masateru (真田昌輝, Sanada Masateru), and others. Baba Nobuharu, age 61 — one of Shingen's most trusted generals — reportedly held the rearguard position to allow Katsuyori to escape, dying in place. It was a career of loyal service that ended with a bullet no samurai of his generation could have imagined facing as a young man.

Katsuyori escaped, but only barely. He was never again able to launch a major offensive. Stripped of territory year by year, he was finally cornered in 1582, his retinue reduced to approximately 50 men, and died by his own hand. The Takeda clan, one of the great powers of the Sengoku (戦国, Sengoku) era, was finished.

Nagashino (長篠, Nagashino) is conventionally cited as the first large-scale demonstration of coordinated firearms tactics in Japanese warfare. Whether Nobunaga actually organized true simultaneous rotating volleys or whether this became an embellishment in later accounts — a debate among historians, notably Stephen Turnbull — does not diminish what the battle proved: that an organized, fixed position with sufficient firepower, properly designed to slow cavalry at a critical moment, could destroy even the finest horsemen in Japan. The samurai ideal of mounted combat, of the individual warrior closing with an enemy, had collided with industrial-scale killing and lost. The result accelerated the shift across all Japanese domains toward infantry-based armies built around firearms, driving daimyo (大名, daimyō) across the country to acquire and train arquebusiers.