A foxhole radio is a radio built by G.I.s during World War II. The foxhole radio differed from the crystal radio. A razor blade and pencil were used as a diode in a foxhole radio while a piece of crystal is used as a diode in a crystal radio. The foxhole radio is like a crystal set in that it does not require an external power source. The radio is powered by the radio frequency that it receives. This made the foxhole radio ideal for the prisoner of war (POW). Prisoners of war made these radios to keep up with current events. Generally, this radio is called so because of the foxholes - small man-made underground shelters used along defensive lines during the war, and so, any radio built during the war can be regarded to be a foxhole radio, but ideally, this radio does NOT use semiconductors