Press ~ during game play to display the console window, then type giftfrompterodon to enable cheat mode. Then, activate the following cheats by entering the corresponding codes. Note: Most of the codes can only be used in single-player mode.

CHEAT FUNCTION - CHEAT CODE
Restore health - chtheal
Restore health for team - chthealteam
Weapon select - chtweap <0-30>
Refill ammunition - chtammo
Get grenades - chtgrenades
Enemies cannot hurt you - chtkostej
Access all quick fight maps - chtallqf
VC and NVA wear Indian masks - chtcannibals
Toggle third person view - cht3pv <0 or 1>
Toggle frame rate display - showfps <0 or 1>
Toggle stat display - showprof <0 or 1>
Mission select - s_all_tasks
Mission skip - s_pass
Unlimited ammunition - s_full_ammo_on
Disable unlimited ammunition - s_full_ammo_off
Invincibility - s_undead_on
Disable invincibility - s_undead_off
Exit game - exit

Use one of the following entries with the chtweap code:

NUMBER - WEAPON
1 - M16
2 - Ak47
3 - (none)
4 - M1 Garand Sniper Rifle
5 - (none)
6 - PPs 41 (Drum Clip)
7 - Colt .45 Pistol
8 - Tarakov
9 - Marakov
10 - .38 Revolver
11 - Remmington Shotgun
12 - Winchester Rifle
13 - (none)
14 - SVD Dragunov
15 - SKS Simonuv
16 - (none)
17 - M60 Heavy Machine Gun
18 - Degterav Machine Gun
19 - US-M3
20 - (none)
21 - Thompson
22 - Silenced Colt .45
23 - PPs 43
24 - (none)
25 - M1 Carbine
26 - Mosin Nagant
27 - M79 Grenade Launcher
28 - Bakiael Shotgun
29 - US Knife
30 - VC Knife

After the first level, when you go back to your bunker go to the shooting range. Go to the supply room. There will be a bottle under the table .Shoot it and music will start. Leave the room and there will be a man standing there, beating invisible drums. He will not die, no matter what you do to him.

Note: The man playing drums is not really invincible. After thirteen grenades from the M79 launcher, he stops playing the drums and falls on the ground. After another thirteen grenades, he dies and just lies on the floor.