WTF i completd mission 2 on halo 3(on co-op) and got no achievement?

[arsenalfan44]

i have the complete mission 1 achievement and i done that solo but then i done co-op and did not get the complete Second mission achievement , why
i am doing it on NORMAL difficlty

 

[lsurocks122593]

Either your playing on the easiest difficulty, which doesn't get you an achievement or you don't get rewarded when you do co-op.

 

[Hello ladies]

You would get it for co-op so you probobly already have it