I was playing Total War Shogun 2 and I watched this little miniclip that talked about the Christian influence in Japan taken in by nanban trade, and how they introduced matchlocks. When were these guns first used? Were they immediately adopted as new technology or did it kind of trickle in? What were the effects?
It's interesting because I quite recently had a similar conversation with a friend, so a lot of this will be what I told him.
So the first battle in Japan involving guns to a significant extent was probably a skirmish between ikko ikki, 'warrior monks', and the Oda, near or otherwise in Ishiyama Honganji - present day Osaka. The actual war itself started because the Ikko Ikki were becoming more and more powerful and Oda Nobunaga wanted, in essence, to weaken their power as it threatened his unification of Japan.
The skirmish itself was led by the young Tokugawa Ieyasu, somewhere around 1560 - 1570. The Ikko had access to matchlocks, however it's important to note that this wasn't controlled or unified, and the matchlocks were used sparingly (at the time, matchlocks were seen as gimmicky or otherwise an oddity in Japanese warfare). Whilst the Ikko had firearms during the battle, the Oda did not. It didn't change how the battle was fought.
The Oda were dealt two defeats by the Ikko (who were using matchlocks), and after this it was essentially proven to Nobunaga that matchlocks were a pretty powerful weapon. The first notable use of matchlocks by a clan against another was the Battle of Nagashino, where, according to Stephen Turnbull in his book Samurai Warfare - Arms and Armour Oda had approximately 3 000 matchlock ashigaru which essentially stopped dead the cavalry charge of the Takeda.
The Takeda were another powerful clan notable for their dominance in mounted warfare, so their defeat essentially started the 'modernisation' of all Japanese armies. So then after this battle (and numerous other ones), around 1580 or so, a significant portion of Japanese armies were composed of matchlockmen. Oda's successor Toyotomi Hideyoshi began his invasion of Kyushu in around 1586 or so by first amassing as much firearms strength as he could.
The Shimazu clan ruling in Kyushu also had access to firearms, as they were really the first mainland Japanese clan to have contact with the first Portuguese matchlocks.
The effects on tactics was drastic. You had lines of matchlockmen firing as such - the first line shot, crouched, reloaded whilst the line behind them shot, rinse and repeat. Military handbooks later on would also incoroporate matchlockmen, or arquebusiers, into their formations (see here - the black circles represent the matchlockmen), as these guns could be used to great effect, most often in the fashion of punching a metaphorical hole through enemy lines for other soldiers to push through.
1543 to have been written and imported guns in Japanese history textbook.
However, this is doubtful.
In other document there is a record of hand cannon was used in Kyoto by men from Ryukyu(Okinawa) in 1466.
Another monk of Kyoto temple wrote he witnessed fire weapon"飛砲火槍" in 1468.
It is correct is written by bigbluepanda on about the using gun effects.
