Mangesh Sawant for Over the Horizon journal:
Electronic warfare (EW) was used for the first time in 1904 during the Russo-Japanese War. The Japanese Navy cruisers Nisshin and Kasuga were coordinating the bombardment of the Russian fleet and Port Arthur, Manchuria. The Russians jammed the radio frequencies of the Japanese cruisers by using EW equipment from the Pobeda battleship and the coastal outpost at Zolotaya Gora. The effectiveness of this countermeasure has been described in a teletype text by Rear Admiral Pavel Petrovich Ukhtomsky to Admiral Yevgeni Ivanovich Alexieyev. Rear Admiral Ukhtomsky writes, “The enemy has fired more than 60 large caliber rounds. No hits on the ships have been recorded.” EW has not received its due importance as compared to fighter aircraft, tanks and warships. However, its importance in warfare is high and its utility, versatile.
The article is a nice introduction to the basics of electronic warfare.