A Legendary Episode - 40G (Original Achievement)
To get this Achievement, you must clear all 5 Chapters of Episode 1 on Legendary difficulty.
You can do this on solo, but it will take a VERY long time and will probably frustrate you.
I suggest gathering a group of friends, or making a boosting session on here and going all out.
There is no need to be scared of dying, you will respawn, even if you are playing solo.
Note: Spartan Ops will cycle through it's Episodes to be playable right away without any planning. However it may not be Episode 1 when you check so you may want to just make your own session.