Your team composition should be pure DPS. It's best to go with 5 Riflemen with decent damage/high mag LMGs (100-200 shots per mag is ideal) so you can constantly spray bullets everywhere without having to keep reloading, but you can probably get away with 1 Sniper and 4 Rifles, provided your sniper is a beast. There's no need for a Medic in this mission, especially if everyone is rocking Warlord gear. You really won't take much damage for about 80% of the op unless you play really reckless.
This mission is actually fairly simple.....right up to the point where the EMP Carrier arrives at the entrance of the tunnel, which is Checkpoint 7 of 8. That's when things get hairy. (There's not much to say for anything before that part, as its really easy. Literally, just shoot everything that moves. I hadn't played this mission before I got the achievement and my group still managed to make it to the very end. Try to keep the Carrier at near max health and that's it. Stay near the truck, shoot for your teammates/watch their backs, and you'll survive.)
When you get to the tunnel entrance, you'll start to run into heavy resistance. Basically, everyone needs to be focused on Bombers (cyborgs carrying big ass red propane tanks) and Mechs. Bombers especially are your main priority. They will ruin your run quickly if they aren't taken out quickly. Watch the ads from the left and right too, don't let them get too close to the truck. Use your grenades! Don't forget about them. They can help take out mobs when you have to reload.
You want to have the Carrier at about 75% health once you hit Checkpoint 8/8. Don't be fooled, there are three more checkpoints once you get here, so stay sharp. As you press on into the tunnel, there will be even more mobs of Bombers and Mechs. Same strategy as before, just focus fire on the Bombers and take out Mechs as quick as you can. Towards the end of the escort, keep an eye on the rear of the Carrier, as there will be enemies attacking from behind and they could be the difference between success and failure.
Once you've safely guided the truck into the hangar, an EMP blast will go off, you will go into a small garage, and the Carrier will explode after about 30 seconds. This is the boss fight. Luckily for you, it is very, very, VERY easy, thanks to a glitch spot. All you have to do is hug the middle wall on the right side of the room. That's it. The boss can't hit you there, and you just have to have one guy watching out for ads coming from the left. With four guys emptying LMG rounds into him, his health bar just melts, and he goes down within 2-3 minutes. Once he goes down, it's over. Congrats! You've beaten one of the easier missions. Now for the HQ op. Just don't forget to prepare your anus before starting it.