[{HVY-E}Jinxx]

You're trying to compare modern radio procedures with those of WWII. In previous combat actions, those before the 1980's, it was quite common to scan for and listen in on enemy radio chatter.
It wasn't until we obtained SINCGARS, (Single Channel Ground and Airborne Radio System), that true radio security was possible. Until then we were still using AN/PRC77's and the like. They could also be encrypted, but not to the extend of SINCGARS.

In WWII, radio communications were at their infancy. Encrypted transmissions weren't really even possible except by the use of codes. In the late 70's and early 80's, the actual transmission frequency was able to be encoded to prevent interception. In the 90's, the SINCGARS upped the encryption by using new keys and by using rotating frequencies on a single channel. This is something that just wasn't possible during WWII.