Japan issued a declaration of war on 8 February 1904. However, three hours before Japan's declaration of war was received by the Russian government, and without warning, the Imperial Japanese Navy attacked the Russian Far East Fleet at Port Arthur.

Tsar Nicholas II was stunned by news of the attack. He could not believe that Japan would commit an act of war without a formal declaration, and had been assured by his ministers that the Japanese would not fight. Russia declared war on Japan eight days later. Japan, in response, made reference to the Russian attack on Sweden in 1808 without declaration of war.