reporter: what you re watching right now is them actually practicing storming a russian trench. this is what they would do to go in and take over an enemy trench. some of them are wearing lasers on their bulletproof vests and when the lasers light up, it means that they re dead. nateem was working at an online retailer before the war. after working the past year, he s now a trainer. it s very important, even for defense. you already know the tactics of your enemy, what they will do. reporter: the front line, of course, is massive, but most of the fighting is happening in incredibly small spaces, just like these, along tree lines, on the counteroffensive front lines. what these soldiers are doing is practicing laying trip wires with grenades on the end, and that is what so much of the combat is right now, both offensively and defensive, finding and laying these trip