The Russo-Japanese War (8 February 1904 – 5 September 1905) was fought between the Russian Empire and the Empire of Japan over rival imperial ambitions in Manchuria and Korea. The major theatres of operations were the Liaodong Peninsula and Mukden in Southern Manchuria and the seas around Korea, Japan and the Yellow Sea.

The Battle of Tsushima (Russian: Цусимское сражение, Tsusimskoye srazheniye), also known as the Battle of Tsushima Strait and the Naval Battle of the Sea of Japan (Japanese: 日本海海戦, Nihonkai-Kaisen) in Japan, was a major naval battle fought between Russia and Japan during the Russo-Japanese War.

It was naval history's only decisive sea battle fought by modern steel battleship fleets, and the first naval battle in which wireless telegraphy (radio) played a critically important role. It has been characterized as the "dying echo of the old era – for the last time in the history of naval warfare ships of the line of a beaten fleet surrendered on the high seas."

It was fought on May 27–28, 1905 (May 14–15 in the Julian calendar then in use in Russia) in the Tsushima Strait between Korea and southernJapan. In this battle the Japanese fleet under Admiral Tōgō Heihachirō destroyed two-thirds of the Russian fleet, under Admiral Zinovy Rozhestvensky, which had traveled over 18,000 nautical miles (33,000 km) to reach the Far East.

In London in 1906, Sir George Sydenham Clarke wrote,

"The battle of Tsu-shima is by far the greatest and the most important naval event since Trafalgar"; 

decades later, historian Edmund Morris agreed with this judgment. The destruction of the Russian navy caused a bitter reaction from the Russian public, which induced a peace treaty in September 1905 without any further battles