 Because obviously you send out a message over the radio, anybody can pick it up. So you put it in code so that anybody who picks it up can't read it. But anybody can break code. I mean, if you can make a code, you can break a code. There's never been a code yet that can't be broken. Germans thought they had one. It turned out they didn't. Japanese thought they had one. Their so-called purple code they thought was unbreakable. Especially if you take proper precautions. One part of which is you change the code every month.