Mission 10: Enemy Lines
This can be done on any difficulty, and whilst it may be possible in Solo, it will be far easier in Co-op.
Towards the end of the mission you will have to destroy the power core of a Kraken (very large ship). You must use a Phaeton (small ship) to get over to the Kraken. Use
to control the altitude of the Phaeton. You may want to destroy all the enemies and turrets before you land. Have one player remain in their Phaeton. Go inside the Kraken and work your way down. You will come across a pair of Banshees (small ships) on a hanger deck, and when you approach them the hanger bay doors will open. Have the person in the Phaeton move alongside the Kraken outside the hanger, so all you have to do is step on to their ship. The power core is down just a little bit further. Destroy it then go back to the hanger and step onto the waiting Phaeton. All players will then get the achievement.
Every mission with combat has two extra achievements. The other one for mission 10 is
You will find a complete list of all campaign achievements in this Solution for All for One in Halo 5: GuardiansDralunt
has this method for getting it done in Solo:Once you enter the hanger bay and see the banshee you can fly it back and to where the phaeton's spawned. Drop it off at the hanger ( not near the door, it may fly out when you trigger the explosion.) and have any of the other Spartans jump in with the cn_up then hop on quick, you don't even need to leave all you need to do is touch the top while an AI is piloting it and the event is triggered. Super easy solo.