The last mission will require multiple playthroughs. First, we're going to kill them all. Be sure to murder every sniper with explosives. Once the reactor has been sabotaged, additional enemies will greet you outside (including a few additional snipers).
The scientists you are asked to extract must be killed! The game will automatically incapacitate them when attempting to kill them with melee strikes. If this happens, reload or restart. Complete the story killing everyone (including military vehicles and pantherturms) as well as the 3 Nazi's that are fairly well hidden. You can find them using the video below.
https://www.youtube.com/watch?time_continue=41&v=uRT...
Completing this mission with no survivors and all snipers dead to explosives will unlock:
We'll cheese through the next playthrough, which should net most of the remaining achievements. It's best to avoid killing anyone, really. The reason is a challenge that requires you to complete the game using only suppressed ammo (Welrod does not count), and a Nazi family we'll spare for an achievement. If you need to kill anyone, make sure it isn't a Reiner and it's with a rifle equipped with suppressed ammo! You can check names by fully tagging the enemy; their identity is located at the bottom. Conversely, you can extract the 3 scientists in another playthrough.
Continue the mission and ensure that all 3 scientists have been extracted. It's tough with limited ammo, but doable. Once the reactor has been sabotaged, exit the bunker without firing a round and run like hell to the exit. Video below for visual reference.
Once complete, you will unlock:
Ah, yes; the challenges... Hopefully you already completed Subsonic, which requires you to finish the mission with only suppressed ammunition. The others include:
Anatomy for Snipers: Land an organ shot every 2 minutes. It's actually not too bad and can be combined with "Did you Hear That?". Headshots do not count, although the brain is technically an organ, but I digress. Go for the lungs, heart, and liver. Just pay close attention to the timer on the challenge page.
Did you Hear That?: Get 40 ghost kills (Can be combined with Anatomy for Snipers)
Field Studies: Kill Nazis with 10 different weapons. You start with three, so just pick up and kill enemies with 7 different weapons. This challenge can also be combined with Research Assistant.
Research Assistant: Recover all research papers in under ten minutes. Just John Rambo this challenge. Combine it with Field Studies for maximum efficiency.
Once completed, you'll unlock:
At this point, you should have unlocked a number of rank achievements throughout the course of your playthrough. These include:
Moreover, a few easy combat related achievements should have been unlocked in the process including: