I'm gonna' say this in behalf of the 67/68 bunch and I'm sure they could contribute greatly. There were a few of us, that sat in the hooches and played music off the ole' reel to reels that had those big 6', air suspended speakers. Sansui and Pioneers. That was the thing back then. Anyway, after drinking we would gather round and someone had the idea to place candles in front of them to watch the adverse effect of sound waves. We would watch the flame dance. After a few tokes on the stuff, well the whole candle could dance. You guys know what I mean. During some of the mortor attacks, you could here the mortors leave the tube and just about tell when you needed to move your ass in your sleep. Then as other can tell you the aircraft reventment was another prime place. CID was operational but must have gotten more active in 68/69. I don't know about you later guys. I don't recall the gas mask routine. Sounds like it would have been more effective though in the ultimate goal. I'll leave it alone for you young guys.