The EE-8 field telephone was used by the US Military from 1935 into the Vietnam War. It used a wired line with a maximum transmission distance of 7 miles. The EE-8 uses D cell batteries to power the electric signal that carries the signal through the wire to the other phone. It has a hand-cranked dynamo to generate the charge that rings the phone on the other end of the line. The case is leather, with fabric insulation covering the cord for the receiver. During World War II the phone was preferred to the radio, and the EE-8 was much more reliable than the backpack mounted Walkie-Talkie (SCR-300) and the Handy-Talkie (SCR-536). The phone line, which could be run through a switchboard from a command center, was often run by soldiers during combat situations.