
Gee, I got the idea from somewhere that devices like this were in common
use in WWII, so that commanders on board ships could bellow at the troops
landing on a beach, for example.

Which reminds me of an anecdote from the mid-60s.  At a communications
conference a Marine Corps communications officer said he didn't care
much for all the spread-spectrum multi-access expensive communication
systems that people were talking about at the time; what he wanted
was a kilowatt broadcast transmitter on the ship and a $4.95 Japanese
transistor radio stuck in the ear of every Marine hitting the beach.
-- 
haynes@cats.ucsc.edu
haynes@cats.bitnet