What can I do with a PAS-6?

Guys, I just picked this up at E-Bay for $25.00 shipped. I bought it because it was dated 1969 and I think it will go well with my display of SOG items. Then again you older guys may have not even used this before. I know that it is a light that runs on two D-size batteries and has a very dark red lens. It is in 'mint" condition and works. Looks like it has two screws on the bottom for attaching to a Gen 1 NVD? It is also built like a tank. I now know that it is an IR illuminator but don't know what for and what the range is? Thanks guys!