question about "decryption"

[Jrog]

I am not sure whether this is AOD or iron cross, I am playing IC over top of AOD.

anyway I am playing Germany 1943 and I see in my battles with the US they are getting a huge +23 or so bonus in the battles due to something called decryption. I understand what it is , but i can't find it nor a way to block it in the game... is it related to signal jamming or intel gathering and such?

thanks!

 

[Conanteacher]

Check out the tech tree.
There are several techs which give you this advantage.
Some are beacuse of radio waves and others because of encryption / decryption techniques.
Read the descriptions carefully.