It's the wheel you've been waiting for! I don't know what "GTA" refers to. Graphic Training Aid? Government Test Acceptance? Grand Theft Auto? And I don't know why it's called a whiz wheel, either. I tried to find out, but all I got was creepy paramilitary websites, so I thought it was best just to back away.
This is from 1975 -- September, to be exact -- and is four inches in diameter. It's made of flexible plastic and has lots of interesting and clever symbols on it. Just dial up the lethal device you're interested in and the wheel does the rest: type of warhead, maximum effective range -- the whole magilla! Of course, the best part about it is that it's called "Societ Weapons Whiz Wheel". I'll bet it was a pretty handy little wheel to have.