You’ll get your first taste of WWI trench warfare while you try to save Petrovich. Advance along the trenches toward the first waypoint. You aren’t really in danger until the very end near the enemy machine gun positions. Just move quickly past them to survive.

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Once you go a bit further, you should see some Russians engaging Germans in the trench. Lean out and shoot the 2 soldiers in the trench. Advance to Dexter to get your new and quite urgent orders. Jump onto the machine gun to save Petrovich as soon as you regain control.
There are a few things that you will need to know for this. This is the one time that friendly fire will matter. The machine gun can kill anyone. Petrovich can also die…if you pour about 100 rounds into him. Trust me. The machine gun will also overheat with continuous fire, so fire in bursts at exposed soldiers.
Your goal is to keep the Germans off of him so that he can escape. Fire into the first line of Germans that form up on the trenches surrounding Petrovich. Then look to the left and finish off the group of about a dozen Germans charging Petrovich. Gun them down carefully, and keep up the fire. Petrovich should fall back to the big fallen tree. Keep firing on the Germans that move up to the other side of the tree. Petrovich should hold his ground for a moment and then run off to the side. Hold your ground and finish off the stragglers. Jump off of the machine gun and follow Dexter to the path as soon as you rout them.