I just cannot seem to get the "Bros to the Close" Achievement. You have to finish the part with all 6 marines alive on heroic or harder. I always seems to lose that 1 marine who decides to rush a knight at the last second.
Its because its included in the Infinity menu. Which is really just the multiplayer menu. I really don't understand why you need live to play it. I'm assuming its because of commendations which you also must be connected to live to obtain