1543: Introduction of Firearms
Firearms arrived at Tanegashima, adding a new option to the military organization of Sengoku lords and local warriors. Their manufacture and use subsequently spread across Japan.
Events this year
8/25
A Chinese vessel carrying Portuguese drifted ashore at Mensura Cape on the southern tip of Tanegashima, and the island's lord, Tanegashima Tokitaka, purchased firearms. This marked the beginning of the introduction of firearms to Japan.
Sources 西之表市「種子島銃（ポルトガル初伝銃）」（市指定文化財）
Month 9
Takeda Harunobu attacked Nagakubo Castle and captured Ōi Sadataka. This represents the process of the Takeda clan advancing from Saku toward the Chisagata District.
Sources 長野県立歴史館「信濃史料」
Yaita Kinbee Kiyosada, the master gunsmith acting on Tanegashima Tokitaka's orders, overcame technical challenges including gun barrel manufacturing and screw-cutting, completing Japan's first domestically-produced firearms within eight months of their introduction.
Sources 鹿児島県「日本初」（鉄砲伝来）
The Ōuchi forces, which had been besieging Gassantoda Castle since Tenbun 11, failed to capture it and withdrew in Tenbun 12 due to Amago Haruhisa's counterattack and defections of local lords. During the withdrawal, Ōuchi Harumochi, Yoshitaka's adopted son and favored heir, died.
Sources 山口県文化振興課「大内氏年表」