This is the only achievement for Halo Anniversary I have yet to unlock. I have tried several times and watched several speed runs online to get some pointers, and I still cannot manage to finish in under 30 minutes. Anyone willing to help get this achievement in cooperative play should send a message to my gamer tag. I am in the Eastern North American time zone and usually free to play on the weekends. Also, I am happy to help anyone with any Halo Reach or Halo Anniversary achievements and cooperative Legendary Campaign runs.