This achievement is for completing chapter 5 named S.O.G. It is story related so there are no special requirements and it is not missable.
As l2ed XIII suggests there is a point where you are being charged by the Vietcong. It is an area filled with trenches at different heights. There are barrels which one of your team kicks over. The game doesn't make it clear you have to knock the rest over here. Do this to progress.