Things are changing up a little bit, since it's our job to help the Germans win the battle. This means fighting against our past work if you want a nice paradox. Spawn in and move down to the sandbags. You can use the machine gun on the Russians if you want. I think it helps limit the number that attack the camp, so go ahead and do it. Just watch out for the guys with auras. The entire bridge should also blow up in a minute. When it does, follow Dexter over to the first German camp. As you're moving, look down the cliff. You should be able to see the Russians moving on the camp. You can safely snipe them from up here. Just fire away at the 9 or 10 soldiers by the sandbags. When I did this, the attack basically didn't happen.
Otherwise, rush down and help the Germans by jumping on a machine gun or sniping from behind the sandbags. When you're done, hit the objective marker and go to the next camp. The Russians have completely overrun the forest, so take your large force and storm the camp. They should be too distracted by the large number of Germans to really target you. Use the rifle from a distance to clear out the left side, then just move through the camp aggressively. It turns to chaos quickly, so keep using the map to find pockets of Russian resistance. Once you take out enough of them, the rest will run away.
You also need to check out the train depot. There might be a few Russians guarding the relevant road, but other than that, it's a clear path to the train depot. It's also still a German position that launching troops, so no climatic battle ahead. Just get to the middle to investigate the artillery hit, and get ready for something completely different.
4 agents should pop in and attack the base. Get behind cover and pop one of the agents in the head a few times. Then switch out your pistol for their pistol. Fire away at the remaining agents to save the camp. They should just have pistols and the Germans will help, so it won't be that difficult.