Complete Campaign mode to unlock Tier One mode.

Reach the following levels in the specified class to unlock the corresponding weapons:

Rifleman class
LEVEL - WEAPON
Level 1 (Recruit) - Assault Rifle: Coalition M16A4, Opposing Force: AK-47
Level 2 (Regular) - Extra Magazine
Level 3 (Expert) - Red Dot Scope
Level 4 (Veteran) - Light Machine Gun: Coalition M249 (Mk.46 Mod 0), Opposing Force: Kalashnikov PKM
Level 5 (Operator) - Suppressors
Level 6 (Commander) - Open-Tip Ammunition
Level 7 (Elite) - Long Range Combat Scope
Level 8 (Tier 1 Recruit) - Muzzle Brake
Level 9 (Tier 1 Regular) - F2000 Assault Rifle
Level 10 (Tier 1 Expert) - Veteran Assault Rifle
Level 11 (Tier 1 Veteran) - Veteran Light Machine Gun
Level 12 (Tier 1 Operator) - Enemy Assault Rifle
Level 13 (Tier 1 Commander) - Pistol Ammo
Level 14 (Tier 1 Elite) - Enemy Light Machine Gun
Level 15 (Tier 1 Warfighter) - Extra Grenade

Special Ops class
LEVEL - WEAPON
Level 1 (Recruit) - Carbine: Coalition Colt M4A1, Opposing Force: Kalashnikov AKS-74U
Level 2 (Regular) - Extra Magazine
Level 3 (Expert) - Red Dot Scope
Level 4 (Veteran) - Combat Shotgun: Coalition Remington 870 MCS, Opposing Force Tula Arms TOZ-194
Level 5 (Operator) - Suppressors
Level 6 (Commander) - Slugs/Open-Tip Ammunition
Level 7 (Elite) - Long Range Combat Scopes
Level 8 (Tier 1 Recruit) - Laser Sights
Level 9 (Tier 1 Regular) - P90 PDW
Level 10 (Tier 1 Expert) - Veteran Carbines
Level 11 (Tier 1 Veteran) - Veteran Combat Shotguns
Level 12 (Tier 1 Operator) - Enemy Carbine
Level 13 (Tier 1 Commander) - Pistol Ammo
Level 14 (Tier 1 Elite) - Enemy Combat Shotgun
Level 15 (Tier 1 Warfighter) - Extra Grenade

Sniper
LEVEL - WEAPON
Level 1 (Recruit) - Battle Rifle: Coalition M21, Opposing Force: Norinco NDM-86 (SVD)
Level 2 (Regular) - Extra Magazine
Level 3 (Expert) - Long Range Combat Scope
Level 4 (Veteran) - Bolt-Action Sniper Rifles: Coalition M24, Opposing Force: Izhmash SV-98
Level 5 (Operator) - Laser Rangefinder
Level 6 (Commander) - Open-Tip Ammunition
Level 7 (Elite) - High Power Scopes
Level 8 (Tier 1 Recruit) - Suppressors
Level 9 (Tier 1 Regular) - G3 Battle Rifle
Level 10 (Tier 1 Expert) - Veteran Battle Rifle
Level 11 (Tier 1 Veteran) - Veteran Sniper Rifle
Level 12 (Tier 1 Operator) - Enemy Battle Rifles
Level 13 (Tier 1 Commander) - Pistol Ammo
Level 14 (Tier 1 Elite) - Enemy Sniper Rifle
Level 15 (Tier 1 Warfighter) - Extra Grenade