I just beat every level on Legendary in halo 3 but it didn't give me the

[Noah]

shield what's wrong?!? i got the achievement for legendary and heroic at the same time. my friend has the normal shield like me but his changed and i do have all the legendary armors.
i got the achievement for legendary and heroic at the same time. my friend has the normal shield like me but his changed and i do have all the legendary armors. we did it co-op with 4 ppl

 

[recklessabandon1433]

dont know dont care ... you would be better off actually doing something with your life than worrying about an icon on halo

 

[Just Human]

um... well if you do, say, half the game on legenary in single player then the rest of the game on legendary co-op it won't work I think, beat every level on legendary in single player, I think that's what you have to do, do it to be safe anyway. Go through the levels again starting from the beginning and see if that works. it should.

 

[QUACK IM A BLENDER!]

same thing happened to me...
sadly it said i did all the missions in co-op (on legendary)
so i just did it by myself on legendary and it finally gave me the achievment
but goodluck
and happy shooting