Head to the Control Tower

You'll finally receive the battle armor, and it will defiantly come in handy during this fight. With it, you can equip three main weapons instead of the standard two. You'll want at least both a good rifle and a rocket launcher. A sniper rifle also works well. As the enemies will already be aware of your presence, there is no need to be sneaky.

Start by defeating all enemies on the roof and continuing down to the zone below. Instead of backtracking to the south, you'll instead need to move north. A large blast gate will start to drop, and you'll need to advance ahead before it closes. The following area is too heavily covered for air support, so you'll need to snipe the enemies with your trusty rifle. Be sure to aim for the gas containers and bridges to destroy the terrain and provide cover.

The final area is not only surrounded by soldiers and turrets, but a full helicopter with missile launchers. Its explosive barrage is brazen enough to even destroy most of the nearby cover, keeping you on your toes. It is imperative to destroy the flying menace with your own rockets and clean up the rest of the foes.

It's not finished yet, as once all of the initial threats are killed, a second wave of five more soldiers will emerge. Take cover, or better yet, man one of the turrets. When it's safe, move to the north and finally finish the mission.