Originally Posted by Crysis Hero
Might be worth mentioning that if you die, you will spawn with non UNSC weapons.
If you die in Co-Op you will respawn without your weapon, therefor losing the achievement. Meaning if on Co-Op you must make it through without dying, which is simple as you can hang back and act as a spawn point for your partner the whole mission. However, on Solo, it is also easy as you may die as many times as you want because you revert to last checkpoint, which will load up whatever weapons you were holding at the time, which should have been a pistol/assault rifle if you were going for this achievement.
In the end, if your a terrible player, you might want to grab the help of a skilled friend who is willing to let you hold back while he/she does the level, but if you are skilled it may be simpler to run through this yourself.