From Rising Sun And Tumbling Bear, by R. M. Connaughton (Orion, 2020), Kindle pp. 63-64:
The Japanese believed that the Hatsuse and Yashima had been struck by Russian submarines. The signal was made, ‘Look out for submarines’, at which point the Shikishima began firing into the sea. Submarines were in the process of being acquired and constructed in both countries but were not used. At the time there was little information in the public domain on the use of submarines. They were introduced into a 1900 Greenwich wargame but an air of uncertainty and caution overshadowed their operation. A contemporary British authority described the submarine as an ‘underhand method of attack’ and recognised it as being detrimental to a nation dependent upon sea trade. A Dutch submarine that featured in a film of 18 July 1904 was purchased by the Japanese. They had been less overt in 1902 when an order was placed for five Holland-design submarines on the American Fore River Company. These thirteen-man, petrol-engined submarines were equipped with one 18-inch torpedo. The boats, built in great secrecy, were sent, dismantled, by rail to Seattle and thence by sea to Yokosuka. They arrived on 12 December 1904, but their assembly was delayed until March–May 1905; eventual commissioning of the first boat on 1 August 1905 was too late for it to take part in the Russo-Japanese War.
The Russians were further advanced than the Japanese in the development of submersibles. The Drzewicki class numbered fifty-two miniature boats, of which the more numerous Type-3 had a crew of four. Employed in the 1877–8 Russo-Turkish War, the boats were designed to fix mines against the hulls of enemy ships. At war’s end, as is the wont of governments, further development came to an end. The boats were used in the close defence of defended localities until 1886, when the majority were converted to buoys. An exception was the three-ton submersible Keta, a modified Drzewicki designed for coastal patrol and fitted with a petrol engine. During the Russo-Japanese War it was beached on the Amur estuary during an abortive attempt to sink a Japanese destroyer.