Helium mode:
Complete Mission 13 Airbase in Firefight under the Elite difficulty setting with a full team, and do not lose a soldier.

Paper mode:
Complete Mission 15 Red Square in Recon under the Elite difficulty setting using only a sniper with the M24 and frags kit.

Black Needle: Easier completion:
Leave Bravo at the insertion/extraction point. Take Alpha and secure the crossroads and rescue the soldiers in the buildings. Make sure you only have one soldier remaining (kill the other two if needed). Go back down the road where about five soldiers are waiting. Let them kill you. If done correctly you should have a mission complete.

Fever Claw: Sniping location:
When playing in multi-player mode, find the large building with a Russian flag flying in front of it. Go through the gate and take a right, then a left, then another left, then turn around. There will be a stairway. Go up it into the building and go up those stairs. Take the first left and you will find a very nice sniping location.

Zebra Straw: Other threats besides artillery:
When you meet up with the allied tank go forward. The first building on the left will have several soldiers in it. One man has an anti-tank rocket. Eliminate him as soon has possible to stop him from destroying the allied tank.

Easy mission completion:
Use the following trick to complete Missions without doing the objectives. Play the mission like firefight mode. Once you kill everybody, the mission is automatically complete with all objectives done.

Start a campaign by selecting "Unassign" to empty all team members. Choose only one man for one team (A or B) if you want an easier Medal of Honor, etc. You can keep a second team as a backup at the insertion point and on hold, suppress and in the prone position (if desired), if your one man is properly equipped with the correct weapons to meet all of the objectives. Before any shooting commences, enter the pause menu and choose "Quick Save". Then, seek and destroy all enemies using only this one man team. As soon as you eliminate an enemy or enemies, pause game play again and do another quick save before continuing your mission. If you should somehow get killed, do not select "Restart" during the mission. Instead, select "Reload" and continue from your last quick save.

On a mission that you are having trouble on, tell the other team to go to a point then follow them. This will help you find where you are supposed to go.

If you are stuck on a quick mission, try these teams. Team Alpha: any three rifleman; Team Bravo: Henry Ramirez (MP5SD, M9 SD), Nigel Tunney (SA80, M136), and Jack Stone (L96A1, M9 SD). First, put Team Bravo in a safe place and do not switch to them until all of Team Alpha gets killed. Try to get as far as you can with Team Alpha before they die, then switch to Team Bravo. You should be able to complete the mission this way.

Medals:
Purple Heart: Get wounded or killed in action.
Bronze Star: Get 15 kills
Silver Star: Get 20 kills
Distinguished Service Cross: Get 25 kills
Congressional Medal Of Honor: Get 30 kills

Bonus characters:
Complete the special objective in the indicated mission to unlock the corresponding bonus character.

Astra Galinsky: Mission 9 Blue Storm
Buzz Gordon: Mission 4 Black Needle
Dieter Munz: Mission 11 Dream Knife
Guram Osadze: Mission 7 Paper Angel under
Henry Ramirez: Mission 5 Gold Mountain
Jack Stone: Mission 3 Stone Bell
Klaus Henkel: Mission 6 Witch Fire
Lindy Cohen: Mission 8 Zebra Straw
Nigel Tunney: Mission 2 Eager Smoke
Susan Grey: Mission 10 Fever Claw
Scott Ibrahim: Mission 12 Ivory Horn
Will Jacobs: Mission 1 Iron Dragon

Successfully complete the first twelve missions in campaign mode to unlock all twelve heroes as playable characters in quick mission and campaign modes. They include Henry Ramirez, Nigel Tunney, Will Jacobs, Jack Stone, Guram Osadze, Susan Grey, Klaus Henkel, Buzz Gordon, Lindy Cohen, Astra Galinksy, Scott Ibrahim, and Dieter Munz.

If you complete the (X) objective for each mission, you will unlock a new soldier. These soldiers have boosted stats and have their own specialist weapons. If these soldiers die, you will not be able to use them except in quick mission mode. You can also use their weapons in multi-player mode.
Cat.

Bonus weapons:
Complete the special objective in the indicated mission and difficulty during mission mode to unlock the corresponding weapon for the indicated bonus character.

5.56 Carbine for Susan Grey: Mission 10 Vilnius under Veteran.
7.62 AR for Lindy Cohen: Mission 8 Battlefield under a Quick Mission.
7.62 Carbine for Will Jacobs: Mission 1 Caves under Veteran.
7.62 Sniper for Astra Galinsky: Mission 9 Swamp under Veteran.
A-91 for Klaus Henkel: Mission 6 Castle under Elite.
AK-74 for Henry Ramirez: Mission 5 Embassy under Recruit.
AN-94 for Buzz Gordon: Mission 4 Village under Elite.
Bizon 9mm for Nigel Tunney: Mission 2 Farm under recruit.
M60 for Dieter Munz: Mission 11 POW Camp under Elite.
M98 for Scott Ibrahim: Mission 12 Docks under Veteran.
PKM for Guram Osadze: Mission 7 River, under Veteran.
Silenced Sniper for Jack Stone: Mission 3 RR Bridge under Elite.

Bonus maps:
Complete campaign mode under the indicated difficulty setting to unlock the corresponding map.

Map MP09 Wilderness: Elite
Map MP07 Stronghold: Recruit
Map MP08 Creekbed: Veteran

Bonus game types:
Complete the indicated mission in Firefight under the Elite difficulty setting using only a sniper to unlock the corresponding game type.

Siege: Mission 5 Embassy
Cat and Mouse Game: Mission 6 Castle
Domination: Mission 15 Red Square

Sniping:
If you are a sniper looking for your enemy when he is hiding in the trees, zoom in with your sniper gun. Look around the trees until the crosshairs turn red. When this happens, you can be almost sure that the enemy is there. You can either shoot him or take out your pistol to save yourself some ammo for your sniper gun, since you are already in position.

When playing in multi-player mode on the city Gold Mt. Level, there is a nice hidden sniping location. In the mission there was a shot down helicopter. To the west will be a strip of the road going down. Go straight ahead. On the front left side is a door. Enter it and go up the stairs to the end of the building. You should be looking out a third story window.

Recommended weapon:
In multi-player mode, choose a rifleman and get Kit 6 (MP5 SD, extra ammunition). This kit will almost win every battle because it has a 30 shot clip and you can walk while looking in the scope. You will have great accuracy with most of the shots. It really does not matter what gun your opponent chooses, unless they select the same kit. The M136 and other powerful weapons take a long time to aim.