Electromagnetic warfare
The intelligence the Japanese gained ultimately led to the decisive Battle of Tsushima, where the Russian Navy lost all its battleships and most of its cruisers and destroyers. These losses effectively ended the Russo-Japanese War in Japan's favor.
During World War II, the Allies and Axis Powers both extensively used EW, or what Winston Churchill referred to as the "Battle of the Beams": as navigational radars were used to guide bombers to their targets and back to their base, the first application of EW in WWII was to interfere with the navigational radars. Chaff was also introduced during WWII to confuse and defeat tracking radar systems.
As battlefield communication and radar technology improved, so did electronic warfare, which played a major role in several military operations during the Vietnam War. Aircraft on bombing runs and air-to-air missions often relied on EW to survive the battle, although many were defeated by Vietnamese ECCM.
In 2007, an Israeli attack on a suspected Syrian nuclear site during Operation Outside the Box (or Operation Orchard) used electronic warfare systems to disrupt Syrian air defenses while Israeli jets crossed much of Syria, bombed their targets, and returned to Israel undeterred. The target was a suspected nuclear reactor under construction near the Euphrates River, modeled after a North Korean reactor and supposedly financed with Iranian assistance. Some reports say Israeli EW systems deactivated all of Syria's air defense systems for the entire period of the raid.
In December 2010, the Russian Army deployed their first land-based multifunctional electronic warfare system known as Borisoglebsk 2, developed by Sozvezdie. Development of the system started in 2004 and evaluation testing successfully completed in December 2010. The Borisoglebsk-2 uses four different types of jamming stations on a single system. The Borisoglebsk-2 system is mounted on nine MT-LB armored vehicles and is intended to suppress mobile satellite communications and satellite-based navigation signals. This EW system is developed to conduct electronic reconnaissance and suppression of radio-frequency sources. In August 2015, the Swedish newspaper Svenska Dagbladet said its initial usage caused concern within NATO. A Russian blog described Borisoglebsk-2 thus:

The 'Borisoglebsk-2', when compared to its predecessors, has better technical characteristics: wider frequency bandwidth for conducting radar collection and jamming, faster scanning times of the frequency spectrum, and higher precision when identifying the location and source of radar emissions, and increased capacity for suppression.

During the first two days of the 2022 Russian invasion of Ukraine, Russian EW disrupted Ukraine's air defense radars and communications, severely disrupting Ukrainian ground-based air defense systems. Russian jamming was so effective it interfered with their own communications, so efforts were scaled back. This led to Ukrainian SAMs regaining much of their effectiveness, which began inflicting significant losses on Russian aircraft by the start of March 2022. Rapid Russian advances at the start of the war prevented EW troops from properly supporting the advancing troops, but by late March and April 2022, extensive jamming infrastructure had been deployed. EW complexes were set up in Donbas in concentrations of up to 10 complexes per 13 mi (21 km) of frontage. Electronic suppression of GPS and radio signals caused heavy losses of Ukrainian UAVs, depriving them of intelligence and precise artillery fire spotting. Small quadcopters had an average life expectancy of around three flights, and larger fixed-wing UAVs like the Bayraktar TB2 had a life expectancy of about six flights. By summer 2022, only some one-third of Ukrainian UAV missions could be said to have been successful, as EW had contributed to Ukraine losing 90% of the thousands of drones it had at the beginning of the invasion.
Russian EW capacity to disrupt GPS signals is credited with the reduction in the success of Ukrainian usage of HIMARS and JDAM bombs. The failure of GPS guidance forces these weapons, in particular JDAMS, to use inertial navigation system which reduces accuracy from around 5 metres (15 ft) down to around 27 metres (90 ft).
Ukraine was losing some 10,000 drones a month due to Russian electronic warfare, according to a 19 May 2023 report by the Royal United Services Institute. This was an average of 300 drones a day. Russia has established EW posts about every 10 kilometres (6 mi) of the front, being some 6 kilometres (4 mi) back from the front line. In October 2023, The Economist reported that electronic warfare was in widespread use on front lines to impair small battlefield UAV activity, with Russia installing video feedback and control jammers on high-value equipment like tanks and artillery. By 11 March 2024, Ukraine reported it had destroyed a Russian Palantin EW system in Zaporizhzhia Oblast, which "suppress satellite radio navigation along the entire line of contact and in most parts of Ukraine, replacing the satellite radio navigation field (spoofing)". An estimated three Palantin systems have been hit (June 2022, February 2023, and March 2024). In addition to the Palantin, in Zaporizhzhia a Layer EW system was destroyed.

In popular culture: In the movie Spaceballs, an electronic attack "jams" a weapons system with a literal jar of jam. In both Top Gun: Maverick and Behind Enemy Lines, characters utilize chaff and flares from their F/A-18s to confuse/deflect guided missiles.

See also: Cyberwarfare
Electromagnetic pulse
Electromagnetic interference
Electronic harassment
L3Harris Technologies
Suppression of Enemy Air Defenses (SEAD)
Other electronic warfare systems:

ADM-160 MALD
Krasukha (electronic warfare system)
Radar warning receiver (RWR)
Samyukta electronic warfare system
Sky Shadow (radar)
Historic:

36th Electronic Warfare Squadron
55th Wing
Battle of Latakia: the first recorded use of deception EW in a naval battle
No. 100 Group RAF
U.S. specific:

Association of Old Crows
DARPA
Electronic warfare officer
Fleet Electronic Warfare Center
Joint Functional Component Command – Network Warfare
National Electronics Museum
U.S. Marine Corps Radio Reconnaissance Platoon
USACEWP (United States Army Computer Network Operations-Electronic Warfare Proponents )

References: 

Citations: 

Sources: 

Further reading: EW 101: A First Course in Electronic Warfare; David Adamy; 2001; ISBN 978-1580531696.
EW 102: A Second Course in Electronic Warfare; David Adamy; 2004; ISBN 978-1580536868.
Deception in War; Jon Latimer; 2001; ISBN 978-0719556050.
FM 3-36: Electronic Warfare In Operations. Safeguarding Soldiers Through Technology. Fort Leavenworth, U.S. Army Combined Arms Center Archived 2011-09-28 at the Wayback Machine (CAC), 26 February 2009 – PDF, 114 p., 4,5 MB. See also: John Milburn: Army manual raises emphasis on electronic warfare. The Washington Post, 26 February 2009.
Jogiaas, Aadu. "Disturbing soviet transmissions in August 1991". Archived from the original on 14 November 2011.
Bolton, Matt; Munro, Matt (2011). "The Tallinn Cables" (PDF). Lonely Planet Magazine (December): 48–55. Archived from the original (PDF) on 2013-11-13.
Winkler, Jonathan Reed (2017). "The Forgotten Menace of Electro-Magnetic Warfare in the Early Cold War". Diplomatic History. 42 (2): 254–280.