Ghost Recon

Sometimes enemies will have two guns in one. You can see strange combinations like a sniper rifle with a grenade launcher on one side, and an AK 74 with a huge snipers scope on the other.

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.

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.
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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

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

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.

Place a claymore in front of a closed door. Backup and detonate it. This will not only blow the door open, but will kill most everyone inside.

When you have a difficult time seeing where your enemies are shooting at you from, send Team Bravo directly in front of you and look which way they are shooting. You will probably lose many men because of their bad aim, but can always restart the level after you know where they are located to easily take them down the second time.

Turn on your night vision to see all enemies within your line of sight.
Adam Curtis.

During any day mission, if you cannot see your enemies turn on the night vision goggles. The opposition will appear as bright white against the lighter green shades of night vision.
Joe Craigle.

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.
OBTrice2008.

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.
SemiAutoHunter.

Usually when you kill every enemy except for one, he will either shoot his gun straight up, or shoot a wall. If you wait about two minutes, about three or four more people will appear. When they shoot the wall or straight up into the sky, they are actually calling for backup. When another soldier far away hears a gun firing, they will run towards it to aid their friends. If you find a group of people and they all are killed except for one, and he begins to sprint away, it is imperative that you catch and eliminate him immediately before it is too late.