What is field telephones?

Field telephones are communication devices used in military and other field operations, usually consisting of two or more units connected by a wire that can be run over a distance of several kilometers. These devices usually have a crank to generate the required electrical current for communication, and a call button to signal the other end. The first field telephones were invented in 1878 by Alexander Graham Bell, and were initially used by military forces during World War I. They are highly durable and designed to withstand harsh conditions, making them an essential tool in battlefield communication. Today, they have been mostly replaced by modern radio communication systems but still remain in use in some areas.