Nothing wrong with the other solutions, but I just did this on chapter 1 and thought I'd share. For the record, I did this on the lowest difficulty and I think this is my first ever solution on TA so please let me know feedback if need be.
After you climb the wall using the rope about halfway through the chapter, you need to pull a switch to let your allies in. Climb down the chain as instructed, then immediately crouch and pick up the health overcharge pack worth +40 health. Don't stop moving forward and a guard will appear from the right, turn right and walk forward. Simply creep up behind him and do a takedown.
If you're quick enough, you can keep going, turn right and get his buddy, who also has his back to you, before overcharge runs out. Or pick up more on the shelf you pass on the right as you approach the second target.
There's also a kampfhund lying down just ahead and a commander in a small room with his back turned to you.
You can use this to farm stealth takedowns/kills on guards, kampfhunds and commanders. I either finished off or did the entirety of the following perks using this method: Knife Throwing, Silent Shot (obviously using the silenced handgun instead of the knife), Vampire, Scout II and Assassin.