Call of Duty: Modern Warfare 2/Homeland Security

Walkthrough
This mission can be soloed, but it helps to have two players in-case one of you goes down.

Start off by picking up an AK-47 Grenadier and going to the alleyway behind the diner, camp in one of the alcoves, shooting any enemies that come through the door or hide behind the cars. When the first Wave is over, pick up an RPG and collect ammo for it, you will not need it on the second wave, but on the third a helicopter comes. In wave 2, a predator drone fires missiles at you if you are outside, stay in the alcove and you will be fine. After you have killed all of the enemies in this and the next wave, there will be a helicopter left, hide in the diner and use the RPGs, the AT4 or just shoot it down if you feel it will be easier. If you really have trouble, there is an ammo crate outside. In the next wave there will be a BTR, sometimes the predator missile destroys this but usually you will have to shoot it with an RPG, as long as you stay out of its sight, it is fairly easy. Use all the previous tactics in the final wave to win.

Option 2: At the start grab the claymores and the first sentry gun on the tarp. There are two sentry guns you can set up. Place one in the backside of the diner behind the barricades with the PDF (Primary Direction of Fire) towards the gas station. Inside the diner is the other sentry gun, place it behind the counter with its PDF out the front of the diner. Grab the SAW off the counter, it's an efficient way to take down the helicopters. Set up claymores at the entrances. Save your RPGs and AT4s for the armored vehicles and helicopters. You can also draw the Predator Drone's fire out front of the diner to eliminate foot mobiles if you get overwhelmed.

Option 3: (one-player) At start, first grab the AK-47 with grenade launcher, then grab the first sentry gun (leave the claymores - to save time and use later) and run towards the front door of Nate's and head to the roof using the interior ladder with the sentry gun. Do this as quickly as possible. Next, deploy the first sentry gun to cover both the interior and exterior ladders to fire at enemy foot mobiles. Grab the claymores on the roof of Nates, grab the second sentry gun and deploy it at the front left corner roof of Nate's. Go back and cover both ladders and eliminate incoming foot mobiles. After you whittle down the foot mobiles from 20 at start to about 7-10 survivors, deploy claymores to cover the ladders, then move the first sentry gun to the right corner roof of Nate's. Just before you leave the roof of Nate's, select better weapons left on the roof from dead foot mobiles (optional), replenish your ammo at the supply dump on the roof, then move quickly to the bank. Deploy and replenish claymores from the bank, grab the third sentry gun inside the bank, and deploy the sentry gun on the grassy hill near the bus stop south of the diner, then go to the diner. The two sentry guns on Nate's roof will give you cover fire. If Wave Two starts before you get back to the diner, a truck-load full of foot mobiles will come in from the north. Destroy it with the AK-47 grenade launcher or sticky bombs. When you get back to the diner, grab the fourth sentry gun and deploy it on a grassy hill just north of the gas station. The two sentry guns on the grassy hills will have interlocking fields of fire. You can defend from the diner or the gas station, moving between each location as the situation requires. With all four sentry guns deployed, you should be able to win this level in just under seven minutes.

Option 4: (one-player) At start, first grab the weapons of your choice, then grab the first sentry gun and run towards Burger Town. Place the sentry gun on the roof of the Burger Town to cover the gas station and the main road. Jump off the roof, run down the entire length of the main road. (You will draw fire from the 20 enemy foot-mobiles. The sentry gun on the Burger Town roof will kill about half of them). When you get near the end of the main road, turn right and run to CRB Financial. Grab the sentry gun and run towards Nate's. (By this time, there will be 5-7 enemy foot-mobiles left). Place the sentry gun on the right front corner roof of Nate's. You'll find another sentry gun on the roof of Nate's. Place that on the left, front corner. Replenish ammo from the supply crate on the roof of Nate's and pickup claymores if desired. Then jump off the roof on left side of Nate's and run to Joe's Diner. Deploy the fourth sentry gun behind the counter, set claymores, and prepare for Round Two. Tips: It's important to place all of the sentry guns on Round 1, as there are no drones or helicopters to shoot at you. Move quickly and keep ammo replenishment and setting claymores to the bare minimum, or else the enemy foot-mobiles can catch up with you. I suggest leaving the claymores at the starting spawn point near the gas station in place for use later. You can grab claymores at Burger Town, CRB Financial, and Nate's.

Tips: Exploding vehicles can kill you. Preemptively destroy any vehicles you run near or might run near with grenade launchers, sticky bombs, or gunfire. Activate the predator drone by running outside, then back inside to safety. When the drone spots you it will shoot and kill foot mobiles (mostly), BTR's (sometimes) and helicopters (rarely). Heavy machine guns can shoot down helicopters. Lighter weapons can shoot down helicopters, but it will take much more ammo to bring it down. Be careful not to walk in front of your own claymores when the enemy is near. Blow up your own claymores first if you find it necessary to move in front of them.

Note: there are also turrets in CRB Financial and on the roof of Nate's but they are hard to get to without two players as the covering fire from the second player is beneficial, there is a lot of risk with going into the open on harder difficulties and as these turrets are not required, it may be best to leave them or go in-between waves.

Secret: There is a third turret hidden on the roof of the building across the road.

Wave 1

 * 20 Hostiles

Wave 2

 * 30 Hostiles
 * Predator Drone armed with Missiles

Wave 3

 * 40 Hostiles
 * 1 Helicopter
 * Predator Drone armed with Missiles

Wave 4

 * 30 Skilled Hostiles
 * 1 BTR80
 * Predator Drone armed with Missiles

Final Wave

 * 40 Skilled Hostiles
 * 1 BTR80
 * 2 Helicopters
 * Predator Drone armed with Missiles