On Lord Of War", the third mission, one of the objectives is to provide cover fire for your downed ally. The frequent RPG fire you will draw from the enemy infantry will make this tougher than it sounds. The best method is to use your missiles to destroy the surrounding buildings where most of the infantry spawn. Shoot the enemies with the FLIR view as they spawn, before they have a chance to move. This is also useful because most of the RPG soldiers fire from the rooftops. Thus, clearing out the buildings will significantly decrease the amount of RPG shots sent your way.