From Rising Sun And Tumbling Bear, by R. M. Connaughton (Orion, 2020), Kindle pp. 70-71:
The intention of foreign nations to learn lessons from the wars of others was demonstrated by the role of the foreign military observer, a role which became institutionalised during the American Civil War 1861–5 and the Franco–Prussian War 1870–71. The alliances which followed-on from these wars and the perceived impact of technological revolution upon modern warfare were responsible for a quantum leap in interest in the monitoring of the events on both sides of the Russo-Japanese War, on land and at sea. There were as many as one hundred foreign military observers from sixteen countries in Manchuria and Korea.
Britain provided the largest proportion of observers for she recognised that, as the ranking power, she had the most to lose in not keeping abreast with the developments and potential of modern warfare. The Royal Navy’s last serious battle had been Trafalgar, 1805, and her army’s last conventional war had been the Crimean War, 1853–6. Colonial conflict, as in the Boer War, 1899–1902, provided Britain with no compelling evidence as to how the next continental war would be fought but what it did do was raise worrying questions concerning the performance of her army. The Imperial Japanese Army had scant regard for the British Army, whereas the Imperial Japanese Navy (and Russia) rated the Royal Navy highly. Even though Captain William Packenham became a personal friend of Admiral Togo, he never felt sufficiently confident to test this friendship by going ashore. Geographical factors provided Britain with further reason to be interested in how the Japanese managed the war. It was the naval strategist Corbett who remarked: ‘What the North Sea and the English Channel are to ourselves, the Sea of Japan and the Straits of Korea are for the island empire of the Far East.’
Russia had good reason to regard as spies the three military observers she accepted from Britain, among whom was Brigadier W. H-H. Waters. Russia was no more relaxed with the Admiralty’s appointee, Captain Eyres, later captured in Manchuria by the Japanese.