Mission 9 Haven's Fall
NOTE: This is the mission you'll have to complete if you choose to side with the Protoss and eliminate the Infected Haven settlers.
1. Build Vikings and a ground force
This mission involves destroying a number of Infested Terran and Zerg bases. This mission (or its alternate Safe Haven), introduces the Viking, an aerial unit that can also serve as a land unit. As soon as you start, build a reactor on your Starport and begin building additional Vikings. Build an Armory and Engineering bay as well while creating a small force of marines to protect the base. Lay down a bunker (or Perdition cannon if you have it) to the north and south with a few Supply Depots to form a wall. You'll be periodically attacked by infested Terran though rarely will they present a threat. Like the previous Outbreak mission, make sure to keep an eye out for Aberrations.
2. Destroy the first Infested structures
Once you've got a few Vikings, clear out the nearest Infested area; take down the Brood Lords and Mutalisks first in aerial form, then switch to assault mode and destroy all the infested buildings, you'll get a message when you've completely cleared the area.
3. Take out the Northeast base
From here, bring the Vikings back and have them repaired while you build additional Vikings and continue to upgrade your ships at the armory. Begin building a small ground force to help your Vikings, as the large bases have anti air turrets in place which can quickly destroy flying units. The ground force needn’t be huge, 10 marines and a medic will suffice. Take out the base in the Northeast first as its large but lightly defended.
4. (Achievement) Protect the colonists
You'll periodically get notices that some of the settlements are being infected. If you're looking for the achievement you'll need to drop what you're doing to help them. To save them you must destroy the Infestor building before it is fully formed. As long as you've got a squad of 7 or so Vikings just follow the method from the first base you destroyed and you should be fine. Kill the Brood Lords and Mutalisks first then clean up after transforming. Note that the settlements can and will be reinfested and you may have to rescue them each more than once.
5. Continue the assault on the Infested structures
The larger bases may require some more ground help to weaken their anti-air defense. A squad of 7 marines, a medic and the two mercenary siege tanks make an excellent ground assault force, as the marines can protect the tanks in siege mode as they safely bombard the bases. Just make sure to call off the siege tanks once you've transformed the Vikings to assault mode to avoid splash damage from the cannons.
As with previous missions, you should be focused on your offense as the attacks on your base should be easily handled by your bunkers and turrets. Once you've cleared the last base the mission is over.