Battlefield 4 Cheats and Tips

Completing the following tasks will unlock the corresponding Multiplayer weapon.
M412 Rex:
Complete the mission 'Baku'.
Shank:
Complete the mission 'Kunlun Mountains'.
Machete:
Complete the mission 'Tashgar'.
QBZ-95-1:
Complete ALL 3 endings for the campaign.
P90:
Complete ALL 3 endings for the campaign.
M249:
Complete ALL 3 endings for the campaign.

Check out the video below if you need help finding the Dog Tags that are scattered throughout the game.
Watch the video
Baku
Dog Tag 1 (0:05) - Nice Play
Dog Tag 2 (0:24) - One Way Trip
Dog Tag 3 (0:46) - Sergeant Dunn

Shanghai
Dog Tag 1 (1:06) - One Man Riot
Dog Tag 2 (1:32) - Going Up
Dog Tag 3 (2:06) - Business Casual

South China Sea
Dog Tag 1 (2:33) - Carcharodon
Dog Tag 2 (2:59) - Lord Of The Waves
Dog Tag 3 (3:21) - Agent Kovic

Singapore
Dog Tag 1 (3:43) - Horizontal Rain
Dog Tag 2 (4:02) - Armored Column
Dog Tag 3 (4:24) - The Grounded Dog

Kunlun Mountains
Dog Tag 1 (4:56) - Cage Fighter
Dog Tag 2 (5:20) - Freedom At Any Cost
Dog Tag 3 (5:46) - Shaw-Shanked Redemption

Tashgar
Dog Tag 1 (6:07) - The Destruction Enthusiast
Dog Tag 2 (6:36) - Upstream Swimmer

Suez
Dog Tag 1 (7:00) - The Rebel
Dog Tag 2 (7:28) - Fleet Guardian