English: An unnamed soldier at the Anzio beachhead during World War 2 holds a foxhole radio, a crude crystal radio. During the war, soldiers were not allowed to use vacuum tube radios, because the regenerative and superheterodyne radios of the time radiated radio waves which would allow the enemy to locate them. Soldiers wanted to listen to radio broadcasts so they built crude crystal radios, which were safe. A common form, shown here, used a blue steel razor blade with a pencil lead pressed against its surface by a safety pin as a detector. The blue oxide coating on the blade formed a semiconductor diode which demodulated the radio signal, extracting the audio (sound) signal from the radio carrier wave. Photo taken for YANK magazine but never used.