At the start of the 20th Century, naval radio was in its infancy. Instead, navies relied on a combination of visual signalling for tactical signals and telegraphs for strategic signalling. Visual signals included flag signals, semaphore and searchlights sending morse code. These were very much limited in range; a ship over the horizon could not be contacted by them. Telegraphs, by contrast, had an almost unlimited range, but could only reach ships in port. This meant that navies were very limited in how they could communicate and operate. Radio changed this, allowing for much more freedom in operational concepts.

The first use of naval radio in wartime came during the Second Boer War. Here, the Royal Navy adopted several Marconi radios that had been ordered by the British Army. The Army had struggled with using the radios ashore, and abandoned them, giving the RN the chance to put them to better use. In March 1900, the radios were fitted to five cruisers, Thetis, Dwarf, Forte, Magicienne and Raccoon, part of the squadron blockading Delagoa Bay. From the RN's viewpoint, this was highly successful; with the ships able to operate out of visual range of each other, the reach of the blockade could be greatly extended. It also allowed for much easier strategic control of the blockade. With one ship retained within range of a shore station attached to the telegraph network, the blockade could act on intelligence sent from the main naval base at Simon's Town (or even from London). This experience, combined with the results of a number of exercises, convinced the RN of the utility of the radio.

Radio allowed for the development of new tactics, which focused on its ability to allow ships, squadrons or fleets to operate out of sight of each other. In the Royal Navy, these tactics centred on the development of 'plotting'. Plotting was a simple concept, capable of being used on both a tactical and strategic scale. In it, intelligence reports of enemy movements were laid out on a 'plot'; essentially, forming a map of the enemy's movements. A commander could then use the plot to work out where to best direct their force. Plotting relied heavily on radio communication, especially on a tactical scale. Keeping the plot up-to-date required frequent reports from the fleet's scouting elements, giving the enemy's speed, course and position. These reports had to arrive almost immediately after being sent to be useful, and radio was the only way this could be done. Radio was also very useful for sending orders down the chain of command to detached squadrons, to ensure they kept in contact with the enemy and could continue to send reports to update the plot.

Plotting worked poorly during WWI. This was due to a combination of technical limitations and poor training. Plotting was limited by the design and quality of early radios. These were 'spark gap' transmitters. These used a spark generated between two cables to create the radio signal. This was a noisy signal, creating a lot of radio interference, even on distant frequencies. This effectively meant that only one ship could transmit at any one time. They were also very vulnerable to damage. Any short circuit in the system would prevent the spark travelling through the antenna. To prevent these forming, the systems were heavily insulated. However, any cut to the insulation would cause short circuits, and disable the radio system. In battle with shell splinters flying everywhere, the system proved unreliable. Meanwhile, the officers that plotting depended on often did not understand their roles in the system. Commanders frequently failed to update their fleet commander on their locations, or the course and speed of the enemy. Most famously, at Jutland, Vice Admiral Beatty, commanding the British Battlecruiser Fleet, sent an incomplete sighting report up the chain to Admiral Jellicoe, in command of the main body of the Grand Fleet. This meant that Jellicoe had to make an educated guess about the approach of the German fleet, rather than being able to infer it from his plot. Ultimately, these problems would be fixed; new radios using vacuum tubes were more reliable and effective, while better training for captains, navigators and signallers helped them to understand their place in the organisation. Plotting was an essential part of naval tactics in WWII, and in a developed form, still exists today.

Another way radio affected naval tactics was through intercepts. Visual signals could not really be effectively intercepted and used for intelligence; it was extremely obvious if another ship was in sight to listen in. Telegraph signals could be intercepted, but it could only be done if the routes of the telegraph cables were convenient. Radio, though, is a broadcast medium, and it is very easy to listen in. Even the most basic forms of radio intercept were useful; traffic analysis, which simply measured the volume of radio intercepts, was very useful for determining when a fleet was likely to sortie. Decrypting or translating messages sent enciphered or in clear could give a clear idea of the enemy's location and intentions. In WWI, the RN's Room 40 helped the Grand Fleet intercept the Germans at Jutland (though several later messages that would have helped Jellicoe pin the High Seas Fleet were not received or were ignored). In WWII, codebreaking played a key role in the Battle of the Atlantic. The German B-Dienst used deciphered British messages to vector U-boats in on Allied convoys; Bletchley Park did the opposite by breaking the Enigma code.