FM 23-10 was the previous version of the Sniper Training manual for the US Army. It has been replaced by FM 3-22 which is a restricted item manual. But the FM23-10 was not. Since I am US Army trained, I am very familiar with this book and it was the one in use when I went through sniper school. It covers all the aspects of sniper training from selection, marksmanship, rifle maintenance, tactics, fieldcraft and many other topics. The Army did come out with an addendum about sniper employment, but I doubt it is included with the copy you buy from Amazon. Keep in mind that this is an Army field manual, it is not written for the general public, so it is not a good “reading” book. Its just stuffed full of useful info.