This was possibly the second hardest mission on Legendary. I had a very tough time on the 360 but accidentally found a very useful strategy this time around!
My strategy for Mission 5: Arcadia Outskirts
The overall focus in order of importance:1. Get your base up and running while balancing defending
2. Knock out the Covenant Mega-Turret
3. Take over a 2nd base and build up to take out the Covenant
4. Surviving the first 5 minutes is key.
My general walkthrough steps:1. As soon as you gain control of your units, select all your units with
and immediately head down the ramp to the left. This will avoid running into the large Covenant crowd on the upper road.
2. Keep urging your troops forwards killing the few Covenant in your path, and then climb the hill South towards the objective. Go up the dirt path, NOT the street to the South!
3. Once in your future base area, use your troops carefully, trying not to lose the Scorpion while taking out the Covenant in the pit.
4. Once the pit is clear, put your Rocket Spartan in the barricades cover on the right side of the Northern entrance to your base, the Laser Spartan in the barricades to the left of him, Forge and your Marines in the Barricades near your base, and the Chain-gun Spartan in the Reactor building that is just on the left along the path you came into the base.
5. Build some Supply Pads then a Reactor, and focus on getting Hornets up as soon as you can!
6. While your base is building, when you first get the base, and periodically through this you will get some reinforcements. Use them to bolster your defenses, although your Spartans should be handling almost everything from the topside. Your left side might need some extra defense though so keep an eye on it. Hunters, Ghosts, Grunts, and Jackals will all come across the overpass. Do make sure your Spartans don't go down otherwise you might get overrun, it's good to sometimes pull them out of cover and back them away to recover. Also, gather all the extra resources lying around..
7. As soon as you start getting Hornets, use them to help out your Spartans and cover the bridge.
8. You want to build up your base to start getting Field Armory Upgrades and especially Wingmen in your Hornets!
9. About now, you should start trying to take out the Covenant Mega-Turret.
10. If your Spartan in the Reactor building is ever in big trouble, relieve him right away, you don't want him to go down!
11. The trick I discovered on this mission is that when you garrison a Spartan in the Reactor building, the mega-turret will focus on him and ignore your base! Otherwise, your base would be simply getting WRECKED by the turret. Also, as far as I can tell, the Mega-Turret can't damage the Spartan in the Reactor! LOL.
12. Try to time your Hornet's attack on the mega-turret right after it fires--otherwise it will shred some Hornets.
13. Keep building Hornets, defending your base, and taking out the mega-turret.
14. Once you've taken out the Mega-turret, it's pretty smooth sailing--take over that 2nd base, build it up with Turrets, upgrade things, get more supplies, and make max Hornets.
15. At this point you may or may not have gotten the reinforcement wave of Spartans--if you did, life will be much easier, but you could possibly start attacking the Covenant base already, focusing on taking out all the Turrets, then hanging out behind it and shooting it to pieces.
16. You will lose Hornets doing this, but you have the backup and bases to wear down the defenses.
17. Take out the Covenant base with all your firepower, and win!