How do you get all helmets in halo3

Some helmets on halo 3 require you to get to a certain rank on online multiplayer, some require you to complete the campaign on certain difficulties (including legendary, but you can do this on solo or co-op), some require certain achievements and others require you to collect all the skulls. I would know as I have obtained all, hope that helps, look on Youtube for more info or guides.
Also I will list the helmets for both Spartans and elites and give info on how to get them.

Spartans: Mark VI (already unlocked), Mark V (get UNSC spartan achievement), ODST (get spartan graduate achievement), CQB (already unlocked), Hayabusa (collect all skulls in campaign), EVA (complete campaign on normal or higher), Security (obtain 1000G on Halo 3), Recon (complete all vidmaster achievements), Rogue (get spartan officer achievement), Scout (get used car salesman achievement), EOD (complete campaign on legendary)

Elites: Commando (get overkill achievement), Aesthetic (get steppin razor
achievement), Flight (complete campaign on Heroic or higher), Assault (already unlocked) , Combat (already unlocked)