March 12, 1926 (Bingyin first month 28) the Dagu events, China's sovereignty has been trampled on.

1926, the Japanese imperialists in Dagu deliberately created a serious incident to trample on the sovereignty of China.
1925 in late December, the Japanese imperialists directly send troops to help Chang Tso-off Guo Songling, support Fengtien again crossed the border to attack the National Army.
1926, the Manchurian warships landing Dagu Beitang repulsed by the national army. National Army to stop Fengtian continue using warships to send soldiers laying mines blockade Dagu and provisions of any ships not open into the foreign ships must also daytime running and accept the Haka. semaphore to stop
3 12 3 pm, two Japanese warships despite national army garrison forts, want to force into the Dagu. National Army immediately sake of making criticisms warning, the Japanese ship was shelling Fort live ammunition, injuring 13 National Army. Fort defenders to hit back in an intolerable situation, the Japanese ship expelled Dagu.
afterwards, the National Army to the Japanese Minister protested anti-Japanese government to destroy the "Boxer Protocol" as an excuse, and openly proposed "protest" and the eight signatory mustered Boxer Protocol " minister, issued an ultimatum on March 16 proposed five unreasonable demands, limited Duan reply within 48 hours. 17, eight warships of the imperialist countries gathered Dagu threat to China. The Dagu events aroused the great indignation of the Chinese people, "three - eighteen events fuse.