Why do we say "Do you copy?" or affirm "Copy that" when communicating via radio, and in the military?

"In the early days when most two-way radio communication used "Morse" code (radiotelegraph), operators used very short 'procedural' signals to save time....Read, as in 'Do you read me", refers to hearing a signal clearly enough to be understood. Copy probably originally referred to writing or typing a received message, but now has is essentially the same as 'Read'."

http://www.dyerlabs.com/communications/procedural_codes.html