Do the following tasks to unlock the following achievements and their alloted gamerscore.

Unlockables

Basic Training (5) Achieve the rank of Private 1st Class
Best of the Best (40) Achieve the rank of Elite
Bomb Expert (15) Defuse the bomb within 2 minutes in Attack & Defend

Coop Hunt Novice (10) Complete a Cooperative T-Hunt mission with at least one other player.
Coop Story Novice (10) Complete a Cooperative Story mission with at least one other player

Dam Buster (30) Completed Nevada Dam in single player Story Mode
Demolition Expert (20) Kill 50 players using Explosives only

Elite Hunter (75) Complete all maps in splitscreen T-Hunt at Realistic difficulty
Equipment Specialist (20) Used all Gadgets at least once in single player Story
Executioner (30) Kill 500 terrorists online or offline

Hazmat Specialist (15) Deposit the canister and kill an enemy canister carrier in the same Retrieval match
Hell Hound (30) Completed Dante's Casino in single player Story Mode
High Climber (30) Completed Vertigo Spire in single player Story Mode
High Roller (30) Completed Calypso Casino in single player Story Mode
Hostage Rescue (15) Rescue all hostages in an Attack & Defend mission in under 5 minutes

Infiltration Specialist (15) Recover the Intel in Attack & Defend within 2 minutes

Killer's Rampage (30) 10 consecutive player kills without dying
Killer's Spree (20) 5 consecutive player kills without dying

Lone Wolf (15) Most kills in a ranked online Sharpshooter match

Marksman (10) 100 total player kills in any adversarial mode
Master of Ceremonies (15) Host a 16-player match

Officer (20) Achieve the rank of Lieutenant 2nd Class

Pistoleer (25) Kill 150 terrorists using only a Pistol

Rainbow Six Legend (100) Complete the single player Story Mode at
Realistic difficulty

Siege Specialist (15) Leading contributor of kills for the Defenders in a winning Attack & Defend ranked match
Sniper (15) 10 kills using a Sniper rifle in an online ranked match
Special Operations (50) Play all maps of every Adversarial game mode
Street Cleaner (30) Completed Downtown Vegas in single player Story Mode
Survivor (15) Be the only remaining player in a ranked online match of Survival

Team Champion (15) Most kills in a winning online ranked match of Team Sharpshooter
Team Survivalist (15) Most kills in a winning online ranked match of Team Survival
Tough Hombre (30) Completed Border Town in single player Story Mode
Tour of Duty (60) Cooperatively complete all Terrorist Hunt missions
True Identity (30) Used the Xbox Live Vision to create a character with your appearance

Vegas Champion (50) Cooperatively complete the Story Mode
Veteran Hunter (50) Complete all maps of splitscreen Terrorist Hunt on Normal difficulty

Ranks - The Following are the Ranks and their unlockables

01 Private 2nd Class All Starting Equiptment
02 Private 1st Class Headgears 1: Tactical Helm, Balaclava
03 Specialist Rainbow Weapons: MP7A1, SIG552, USP40
04 Corporal Camo 1: Desert, Urban, Russian, Guerrilla, Fall, Desert 2
05 Sergeant Tactical Armor: Raven Recon Armor, Vulture Combat Armor, Falcon Assault Armor
06 Staff Sergeant Headgears 2: 3 Hole Balaclava, Baseball Cap, Breathing Mask
07 Sergeant First Class Camo 2: Flecktarn, Orange, Swedish, War2k5, Alpen, White
08 Master Sergeant Freedom Fighter weapons: AK47, Raging Bull, SV98
09 First Sergeant Headgears 3: Bonnie Hat, Beret, Tinted Goggles
10 Sergeant Major Black Market Armor: Typhoon Recon Armor, Cyclone Combat Armor, Hurricane Assault Armor
11 2nd Lieutenant Camo 3: Pink, Blue, Woodland, Wasp, Sand, Crimson
12 1st Lieutenant Headgears 4: Half-Face Mask, Reinforced Helm, Tactical Goggles
13 Captain Merc Weapons: MG36, SPAS12, Deagle
14 Major Military Armor: Vier Recon Armor, Diamondback Combat Armor, Anaconda Assault Armor
15 Lt. Colonel Camo 4: Yellow Urban, Red Urban, Tiger, Rust, Urban 2, Grey
16 Colonel Headgears 5: Ballistic Face Mask, Riot Helm, NVGs
17 Elite Camo 5: Custom 1, Custom 2, Custom 3