Setting: late Muromachi / Aizuchi-Momoyama, Japan mid-late 16thc
* Lorge 2008 p54
"The spread of war outside of the capital, and the more generalized breakdown of the pre-existing social order, vastly expanded the total number of men involved in fighting and gave rise to increasing numbers of sieges. Given the limited number of horses in Japan, let alone the changing nature of warfare, the growth in army size virtually mandated that infantry play a greater part in campaigns. The rise of infantry, in turn, opened the door to advancement for less wealthy members of the warrior class, and even men from outside the warrior class. This was something of a social revolution, but guns had nothing to do with it.
"The Warring States period was brought to a close by an escalating series of campaigns fueled in no small part by the growing population and economy of the sixteenth century. As army size increased, the quality of individual soldiers decreased. Armies took on larger numbers of ashigaru (lit., 'light-foot,' less heavily armored troops of the lowest martial class, or commoners pressed into service) and untrained men to add mass to their formations, all them to maintain sieges, and extend their range of operations. Cavalry and well-trained samurai still played an important part in operations, if sometimes for no reason other than the military culture of the commanders, but minimally trained infantry grew in significance. Commanders and political leaders developed the administrative, strategic, and tactical means to raise, pay, supply, and deploy these armies, which had now moved well beyond the small bands of elite troops skirmishing on horseback. Without these changes in warfare, or indeed before they had taken place, guns and handguns could not be effectively used in battle."
* Art of the samurai 2009 p23-24 (Ogawa Morihiro, "The Spirit of the samurai" p3-35)
"Warfare in the middle and late Muromachi period was conducted by groups of infantry in combat at close quarters. The yari, which had been but sparsely used in the late Kamakura and Nanbokuchō periods, now became a weapon of major importance, and many famous pieces have survived from that time. Then in the twelfth year of the Tanbun era (1543), guns arrived in Japan -- in a Portuguese boat blown off course on its way to Okinawa (an alternate theory holds that guns were introduced to Japan from China before that time by Japanese pirates, or wako). In the blink of an eye, firearms had spread across Japan, and they soon had a significant effect on castle architecture and military strategy. Lightly armed foot soldiers called ashigaru became the common fighting force. They were formed into divisions, some in companies equipped with matchlock guns and others in conventional companies carrying yari. The matchlock companies would fire at the enemy, and the yari companies would attack them during the ensuing confusion, after which swords would be used by all combatants. The first battle in which guns were used in large numbers was at the fortress in Nagashino (Aichi Prefecture) in 1575, when the combined forces of Oda Nobunaga and Tokugawa Ieyasu (1543-1616) fought against Takeda Katsuyori (1546-1582), a shugo daimyo. The combined Oda-Tokugawa army, possibly armed with as many as three thousand guns, gained a resounding victory. Nobunaga then proceeded to destroy the Takeda family in 1582, opening the prospect of conquering the entire country."
* Lorge 2008 p54-55
"... [G]uns and handguns had been available in East Asia for three centuries before the Portuguese and Portuguese-style arquebuses became important in Japanese warfare. The growing role of poorly trained infantry now provided the demand for the new weapons. The introduction of Portuguese arquebuses to Japan is traditionally dated to 1543, by which time the Warring States period had long been under way. These weapons spread rapidly throughout the country as warlords contending for power sought any advantage over their rivals. But since no individual warlord or even faction had a monopoly over the new weapons, any advantage was relative rather than absolute, and also likely transitory. What the new weapons did was make lower-quality infantrymen much more effective in battle. Good strategy and tactics were still critical, however, in combining the arquebus into the existing modes of fighting in a useful way."