first tier:

Lightweight – move faster than normal.
Pro = Prevents damage from falling.
How to get pro:
Achievement 1: Escape Death: Escape death 5 times after being shot. 
Achievement 2: Melee Kills: Get 15 melee kills. 
Achievement 3: Offense Medal: Get 10 offense medals by killing enemies near their objectives.

Scavenger – resupply from dead bodies.
Pro = Extra magazines; resupply tactical grenades.
How to get pro:
Achievement 1: Get 5 kills without dying 5 times
Achievement 2: Get 5 lethal grenade kills with resupplied grenades
Achievement 3: Resupply 150 times with scavenger

Ghost – undetectable by Spy Planes.
Pro = Invisible to aircraft and turrets; No red crosshair or name when targeted.
How to get pro:
Achievement 1: Concealed Kills – Kill 20 enemies while they have a Spy Plane or Blackbird active.
Achievement 2: Destroy Aircraft – Destroy 30 aircraft with any non-Killstreak launcher.
Achievement 3: Destroy Sentry Gun – Destroy 1 Sentry Gun.

Hardline – gain Killstreak Rewards with one less kill to normal.
Pro = Re-roll the result of a care package.
How to get pro:
Achievement 1: Earn and call in attack dogs
Achievement 2: Get a 7 killstreak
Achievement 3: Share 10 care packages with teammates

Flak Jacket – enhances your resistance to explosives.
Pro = Immunity to fire damage; Reset grenade timer on toss back.
How to get pro:
Achievement 1: Plant/defuse 10 bombs in demolition
Achievement 2: Survive 10 explosions
Achievement 3: Throw back 5 enemy grenades


second tier:

Hardened – increases the penetration of your bullets.
Pro = Increased damage to aircraft and turrets; Reduced flinch when shot.
How to get pro:
Achievement 1: Get 10 kills through walls
Achievement 2: Destroy 1 pieces of enemy equipment through walls
Achievement 3: Shoot 200 bullets into enemy aircraft

Scout – allows you to hold your breath for longer than normal.
Pro = Switch weapons faster.
How to get pro:
Achievement 1: Secondary Kills – Get 50 kills with secondary weapons
Achievement 2: One Shot Kills – Get 50 One Shot, One Kill Medals
Achievement 3: Headshots – Get 30 Headshot kills

Steady Aim – increases your hipfire accuracy.
Pro = Faster weapon raise after sprinting; Faster knife recovery.
How to get pro:
Achievement 1: Get 150 hip-fire kills
Achievement 2: Melee 2 enemies consecutively 3 times
Achievement 3: Get 100 kills after sprinting

Sleight of Hand
 – you to reload faster than normal.
Pro = Aim down sights faster with non-scoped weapons.
How to get pro:
Achievement 1: Get 150 kills while ADS
Achievement 2: Reload and finish off the enemy you wounded 10 times (shoot, reload, kill X10)
Achievement 3: Kill an enemy within 5 seconds of reloading 30 times

Warlord – additional primary weapon attachments.
Pro = Allows you to start with additional lethal/tactical grenades.
How to get pro:
Achievement 1: Get 25 frag or semtex kills
Achievement 2: Get 1 multi-kills with grenades
Achievement 3: Get 150 kills using guns with two attachments


third tier:

Hacker - allows you to detect enemy equipment and explosives.
Pro = Sabotage enemy equipment, turrets and crates; makes you invisible to motion sensors.
How to get pro:
Achievement 1: Destroy 25 equipment or explosives using hacker
Achievement 2: Kill an enemy with claymores or c4 25 times
Achievement 3: Kill 25 enemies within jammer or motion sensor radius

Marathon – allows you to sprint longer than normal.
Pro = Gives you unlimited sprinting power.
How to get pro:
Achievement 1: 26 Miles – Sprint 26 miles using Marathon.
Achievement 2: First Blood – Get the First Blood Medal 10 times.
Achievement 3: Captures – In Capture the Flag, get the Flag Capture Medal 15 times while using Marathon

Ninja – gives you silent movements!
Pro = Louder enemy footsteps.
How to get pro:
Achievement 1: Get 5 backstabber medals
Achievement 2: Plant the bomb in search and destroy, demolition or sabotage 10 times
Achievement 3: Get 150 kills using the suppressor attachment

Second Chance – pull out your pistol before dying so you can get some revenge before you kick the bucket!
Pro = Longer down time; any friendly can revive you.
How to get pro:
Achievement 1: Get 1 headshot kills in second chance
Achievement 2: Get 10 kills in second chance
Achievement 3: In second chance, kill the guy who downed you 5 times

Tactical Mask – protects you against Nova Gas.
Pro = Resist flash/concussion grenades; reveal position of flashed/stunned enemies.
How to get pro:
Achievement 1: Kill 20 enemies that are stunned by your concussion grenade
Achievement 2: Kill 20 flashbanged enemies by your flashbang
Achievement 3: Kill 20 enemies poisoned by your nova gas