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Military results

Russia had lost two of its three fleets. Only its Black Sea Fleet remained, the result of the 1878 Treaty of Berlin which had prevented the fleet from leaving the Black Sea through the Bosphorus, since Turkey and Britain would not waive the relevant clauses. The Berlin treaty superseded the London Straits Convention of 1841, which had been favourable to Russia.

Japan became the sixth-most powerful naval force by combined tonnage, while the Russian Navy declined to one barely stronger than that of Austria–Hungary. The actual costs of the war were large enough to affect the Russian economy and, despite grain exports, the nation developed an external balance of payments deficit. The cost of military re-equipment and re-expansion after 1905 pushed the economy further into deficit, although the size of the deficit was obscured.

The Japanese were on the offensive for most of the war and used massed infantry assaults against defensive positions, which would later become the standard of all European armies during World War I. The battles of the Russo-Japanese War, in which machine guns and artillery took a heavy toll on Russian and Japanese troops, were a precursor to the trench warfare of World War I. A German military advisor sent to Japan, Jakob Meckel, had a tremendous impact on the development of the Japanese military training, tactics, strategy, and organization. His reforms were credited with Japan's overwhelming victory over China in the First Sino-Japanese War of 1894–1895. However, his over-reliance on infantry in offensive campaigns also led to a large number of Japanese casualties.

Military and economic exhaustion affected both countries. Japanese historians regard this war as a turning point for Japan, and a key to understanding the reasons why Japan may have failed militarily and politically later. After the war, acrimony was felt at every level of Japanese society, and it became the consensus within Japan that their nation had been treated as the defeated power during the peace conference. As time went on, this feeling, coupled with the sense of "arrogance" at becoming a Great Power, grew and added to growing Japanese hostility towards the West, and fuelled Japan's military and imperial ambitions. Furthermore, Japan's substantiated interests in Korea and Liaodong led to the creation of a Kwantung Army, which became an autonomous and increasingly powerful regional force. Only five years after the war, Japan de jure annexed Korea as part of its colonial empire. Two decades after that, the Kwantung Army staged an incident that led to the invasion of Manchuria in the Mukden Incident; the Kwantung Army eventually came to be heavily involved in the state's politics and administration, leading to a series of localized conflicts with Chinese regional warlords that finally extended into the Second Sino-Japanese War in 1937. As a result, most Chinese historians consider the Russo-Japanese War as a key development in Japan's spiral into militarism in the 1920s–30s.

Following the victory of the Battle of Tsushima, Japan's erstwhile British ally presented a lock of Admiral Nelson's hair to the Imperial Japanese Navy, judging its performance then as on a par with Britain's victory at Trafalgar in 1805. It is still on display at Kyouiku Sankoukan, a public museum maintained by the Japan Self-Defence Force. Nevertheless, there was a consequent shift in British strategic thinking, resulting in enlargement of its naval docks at Auckland, New Zealand; Bombay, British India; Fremantle and Sydney, Australia; Simon's Town, Cape Colony; Singapore and British Hong Kong. The naval war confirmed the direction of the British Admiralty 's thinking in tactical terms even as it undermined its strategic grasp of a changing world. Tactical orthodoxy, for example, assumed that a naval battle would imitate the conditions of stationary combat and that ships would engage in one long line sailing on parallel courses; but more flexible tactical thinking would now be required as a firing ship and its target manoeuvred independently.