So for this achievement, you need to finish a mission on legendary, without firing any shots or grenades.
I have completed Uplift Reserve twice now. Both times I followed the rules. But nothing. I dont have any sign of it working. Any reason why>
3rd time 
Still nope.
Hey there!
When you look at the achievement in the Xbox One achievements app, does it show the words “Done! Unlocking…”? If so, then you don’t need to do anything other than wait. This is out of everyone’s hands, as the Xbox One achievement system is server-based, not local. This means that an unlock request to the server can fail, leaving the achievement in the “Done! Unlocking…” stage until the request is successfully resent. 
If the achievement does not show the above message, then you may have to try again, sadly. If you’ve done it 5 times and it doesn’t unlock, I’ll let 343i know. My friend had to attempt Classic twice before it worked. Make sure you never touch the right trigger, even while boosting the Ghost.
I hope this helps.
It doesnt say the Done Unlocking thing.
I will go and try it again however.
Just done it again, for the 4th time. Finally worked. 
> 2533274924290830;5:
> Just done it again, for the 4th time. Finally worked.
I’m very happy to hear this. Sorry it took four tries, but at least it finally unlocked!
If you need anything else that’s Support related, feel free to make a thread, or you can P.M. me as well.