Tip of the Spear - Rolling Thunder

Escort the Assault Derricks to Landown

Now this is what we're talking about, heavy artillery baby! While you may not be able to drive her, it's up to you to defend her. Grab hold of the turret at the top of the ramp and learn to love it, as this should be your primary weapon for the duration of this mission. Although it has unlimited ammo, be easy on the trigger, as it will overheat if used too much, killing precious time while it cools down.

Shoot Down the Nemacyst Mortars

A little ways into your trip, you'll come under fire by incoming projectiles. If too many collide with your ride, it's game over. As such, you need to shoot them before they hit by leading your shots—that is, follow the smoke trail and shoot where they will be in a second or two (your shots are too slow to try and fire at them directly). There's nothing you can do about the first few, but you need to get on the defensive shortly after the helicopter goes down. Just be careful that you don't hold down the trigger for too long, otherwise the gun will have to cool off, which may not give you enough time to target the incoming rocks.

Kill All Incoming Reavers

If it's not flying rocks, it's flying Reavers. Now despite what the objective says, you only have to kill one: The one that tries to ram your ride off the road, from the left. Use your turret and target the two riders on the Reaver's back, then focus your attention on the Reaver himself. You have to move fast, otherwise he'll knock you off the cliff.

Take cover here as soon as the enemies on the ridge appear.

Defend Dizzy While He Repairs the Assault Derrick

Oh great, what now? It seems Derrick wasn't built to slide-down hillsides at high speed, so you're going to have to defend Dizzy while he repairs the vehicle. First, grab the ammo boxes and grenades to your left, near Derrick's front wheel. Now immediately seek cover behind the closest fallen pillar (ideally, to the far left of it), as the enemies are going to climb out of their emergence holes ahead. If you're handy with your grenades, try chucking them into the emergence holes (near the middle of the back area) to close it up, then a second to the right. If not, just hang here and shoot the enemies from behind you're cover. Once they're down, more will flank you from a ledge on the right—reposition yourself behind the left side of the pillar for cover, but get ready to move back again when more enemies appear in their original location.

Climb Back On Board the Assault Derrick

Get ready to bolt back to your ride as soon as Dizzy reports the rig as fixed.