This achievement is earned by completing the 7th mission called Reunion on any difficulty (though for the other 2 achievements listed below you are required to play on at least Heroic difficulty). If you are playing through the campaign it is unmissable and is the 2nd mission where you take control of the Master Chief.
At the start of the mission it will be a peaceful walk through an unexplored world but you quickly encounter Covenant. There are a couple of small patrols but the 3rd patrol has a Phantom with them. Destroy that and you also unlock:
Continue through the mission activating the consoles, there are 3 in total. Just before the third one which you can see in the distance you again bump into the 'Boss' and must defeat him before you can continue.
Activate the 3rd console and then its just a case of passing through a final cave to reach the end location. Its worth noting that in the cave there are 2 paths, the right one consists of flying Phaetons through it, however the left one involves walking through it and using man cannons. Complete the left path and you also unlock:
Reach the end of the cave and then wander forward a bit further and the mission is complete