Communication was vital on the World War I battlefield, and when it broke down the results could be fatal. Units at the front line needed to know where their neighbours were, while commanding officers working behind the lines could only control their men if they had a reliable source of information. Fought between 1914 and 1918, WWI took place on a massive scale. The men who served in the conflict used various methods of communication. Some used the most up-to-date technology of the time while others dated from more historic conflicts.
Telephones allowed units on different parts of a WWI battlefield to communicate with each other. Long wires linked the telephones with each other via switchboards. The system was reliable as long as the wires remained intact. Since the trenches were the only place to string phone wires, the wires frequently broke for causes that ranged from the clumsy feet of careless soldiers to enemy shellfire. When an army advanced, a team of soldiers would bring the telephone line forward and set up communication posts in the trenches captured from the enemy.
Radio was widely used in WWI. Combatant armies used mobile radio devices capable of transmitting and receiving Morse code, but they were bulky, often too fragile for trench life and had a very limited range. Radios were much more widely used at sea, where they allowed ships and submarines to communicate with each other and receive orders from their bases on land. Technological developments during the war began to allow ships to pinpoint the location of enemy craft using their radio transmissions. During the war the National Institute of Standards and Technology developed a prototype location system used by the U.S. Navy.
Major armies also relied on much less technologically advanced means of visual communication to send messages. Until 1915 the British army used an adapted paraffin lamp known as a "Begbie" to send messages via Morse code, using a special lens to concentrate the light into a more powerful beam. This was an insecure method of sending information since anyone who could see the light could intercept the message. The British also used signalling flags to send information. A skilled operator could signal around 12 words a minute.
All major combatant armies in WWI used carrier pigeons to transport messages. The birds used their homing instincts to carry routine messages and information in the heat of battle. In a battle situation they provided a way of getting vital information to commanders when telephone lines were absent or broken. In 1918 a pigeon called Cher Ami received the French Croix de Guerre medal for carrying a message from an isolated group of American soldiers giving their location. The information allowed nearby units to mount a rescue mission, saving the lives of 194 members of the 77th Infantry Division.