"I worked in the office mostly on the SI's. Those were the small packets
that listed our helicopter companies throughout the theater and the
ground troops throughout the theater or at least where our helicopter
gun ships went. The list was changed every week and had to be sent to
each company...ground and our helicopter support gun ships. The list gave
the new call sign and frequency for each every week. This, of course,
was for security. I also worked sometimes in the cryto-teletype
room sending and/or receiving messages."