Bros to the Close Achievement in Halo: The Master Chief Collection

This achievement is best obtained when playing on the Heroic difficulty with three cooperative partners. In addition to this, you can opt to start the mission at Rally Point Bravo, as doing so will place you in the mission just after the cutscene where Lasky and Palmer are introduced.

At this time, you will need to complete the next objective without allowing any Marine allies to die. After emerging from the structure after the cutscene, two Marines will fight by your side. You will need to kill a small wave of Promethean enemies and advance up a winding path where another swarm of Crawlers and Knights are stationed. As a general note, approach these first two firefights offensively. Don’t be hesitant in rushing into the line of fire and dispatching the enemies with close-quarter means. Once the Prometheans here are dead, double check that both Marines are still alive.

After climbing down the winding path, you will reach another squadron of four Marines that are under attack by Prometheans on the hillside ahead. Be sure to utilize a ranged weapon such as the Battle Rifle or Light Rifle in picking off the Crawlers, Watchers, and Knights that are ambushing the Marines. Once this initial wave of enemies has been cleared, climb the hillside and insert Cortana’s AI chip into the nearby console when she gives you the command. At this point, you will now have to fend off the hillside from three or so waves of Prometheans forces. Make sure to utilize the mounted machine guns, Railgun, grenades, and any other weapons at your disposal during this massive firefight.

Once Cortana has successfully opened the door and the enemies have been killed, the achievement will unlock so long as all six Marines are still alive. If for whatever reason the achievement hasn’t unlocked or a Marine has died at any point during this entire section of the mission, you can always revert your save to the last checkpoint and try again. Remember, doing this with three cooperative players will prove to be much easier than trying alone.