Imagine Katyusha. Now replace the boring small rocket with a bigger one. When it hits the target it emits a large cloud of combustible vapour which gets into everything: bunkers, trenches, inside vehicles, your own lungs, whatever. Then it explodes and creates a vacuum causing a huge shockwave which rips apart everything it meets with high power. That’s what ТОS-1 is. The acronym actually translates to Heavy Flamethrower System (Тяжелая Огнеметная Система). As you can say, very effective at clearing out any kinds of defensive positions.