Museum of Portable SoundFoxhole Radios date back to the 1890s but were most popular during WW2. Soldiers couldn't use vacuum tube radios bc their radio waves could be traced by the enemy, so soldiers built safe but crude crystal radios like this one at the Anzio beachhead in Italy in 1944, which used a blue steel razor blade with a pencil lead pressed against its surface by a safety pin as a detector.
Learn to make your own foxhole radio here:
Anon User