I send everyone to sleep. The MkII is my favoured weapon. Silent, efficient, accurate, and stops respawning. that said, at the hardest difficulty, the soldiers get back up pretty quickly.
However, as as I said, for this battle, you can just hide under the truck at the left of the map near the beginning. No one can see you under there at all, and you can snipe silently in NV mode for as long as you wish without impediment. It makes this battle pretty easy (although fairly lengthly), and has the bonus of not being exposed to the weather.







