First PNG I saw was in 1975 on 103 Sqn in Singapore. One of our crews used them to descend into an upcountry clearing and sat there all night checking on how accurate the rest of us were at night navigation over the jungle. Most of us got within several hundred yards which was pretty good with only a clock, compass and maps marked "uncharted territory". The procedure was that one pilot had the goggles strapped on and flew the ac but he couldn't see any of the instruments and the other had to sit in complete darkness, read out things like, height, speed, attitude, rod and be ready to turn the cockpit lights on and take control in the event of an emergency. The crewman then did all he could to navigate (he was the only one who could see the map) and just about everything else! Changing radio frequencies was a nightmare. It was about 1977-8 when we were stopped from using them in N. Ireland after a series of very hairy incidents which bent a few aircraft and any one of which could have been a nasty accident.