Gathered all 12 pages of the Valhalla Report
You must gather all 12 page from the Valhalla Report scattered throughout campaign missions 13 to 25. Finding these reports unlocks the Eagle's Nest missions. You will not be able to unlock all Eagle's Nest achievements or the "Military Cross"and "Medal of Honor" without collecting all of them. Valhalla Reports are found on the bodies of enemies that you kill. You must pick it up from their corpse, which is done by going next to them and choosing "pick up" from the Action Menu.

The reports are always on a specific enemy type for each mission, but the exact enemy is picked at random. For example if I say that the Valhalla Report is on a Panzer Demon it will always be on a Panzer Demon, but it could be on any Panzer Demon on the mission. The reports are usually on one of the specified enemies in the first wave (the enemies on the map that you first face), but not always. Make sure you are thorough in your search.

Here are where the Valhalla Reports are found:
13- W Heer Schutze.
14- W Heer Schutze.
15- Waffen-SS Magier.
16- Waffen-SS Schutze.
17- Waffen-SS Schutze.
18- W-SS Panzer Demon.
19- Waffen-SS Vampire.
20- Waffen-SS Schutze.
21- Waffen-SS Vampire.
22- Waffen-SS Schutze.
23- Waffen-SS Magier.
24- Waffen-SS Magier