Take a look here -> http://members.aol.com/djadamson7/articles/foxhole.html or do a search for foxhole radios.

These are the old "foxhole" radios that were common in WWII. I know that this is a receiving radio, but this maybe be a starting point for your search. I read a website a while ago, that described a POW in Japan turning one of these into a transmitter, but lack of coffee keeps me from remembering where I found it.