I'm confused with the ranking in Halo 4

Is the armor unlocking system Halo 3 style or Halo Reach style? How do you unlock the Mark VI helmet?

Some armors are unlocked through leveling up in ranks, specializations, unlocking achievements, completing Waypoint challenge, and completing commendations. I guess the style is new which is the Halo 4 style.

This^ and you unlock full MK VI not just the helmet for beating the game on legendary from what I’ve heard.