Sniper Elite V2

Simply sneak up on guards who are unaware of your presence and press A when prompted. Remember to crouch when moving in for the kill otherwise if you're standing up you will make too much noise.

This can also be done sniping or with the Welrod close up but the main thing to remember is that they need to be unaware of you.

To get this achievement you need to get close to the enemy first press B to crouch so you have quieter footsteps once you are close enough it will say press A on screen on bottom left hand side to stealth kill complete this 25 times achievement is yours also if you are in prone (lying down) you can't stealth kill.

FASTEST WAY TO GET THIS ACHIEVEMENT!!!!! is on the prologue mission. Play through the level till you get to the part where you're required to shoot and kill the general. Everyone is getting the "FRONT AND CENTER, PASS THE BUCK, and DEAD EYE achievements here. Simply just shoot the pillar twice which is next to the men talking (first shot hardly ever kills the target) shot will ricochet off the pillar and kill the person. This counts as a silent but deadly kill. Shoot the general in the head and RESTART TO CHECKPOINT. Do this twenty five times and the achievement will unlock. The pillar shot is tricky at first, but gets easier the more you do it. This is confirmed by me, because this is how I got the achievement.

I actually popped this one on the level where I had to blow the explosives to stop the convoy. I messed up my first shot so when I took my second shot it blew up the truck carrying the target and a bunch of soldiers. I'd already stealthed a few but blowing up the truck counted as a covert assassination.