There are a total of 35 collectibles (Dog Tags & Weapons) in Battlefield 4. Finding all of them will earn you the Recon trophy / achievement and counts towards “Full arsenal”. The collectibles are divided in two categories: 19 Dog Tags & 16 Hidden Weapons. You can see how many you’ve found by pausing the game during a mission, or by checking out your progress in mission select.
After picking up a collectible it will be saved automatically and immediately. You don’t have to pick it up again if you die. You may also leave the game immediately after finding one, without having to reach the next checkpoint. Your progress will still be saved.
Picking up weapons from dead enemies does also add up to your collectible progress towards “Recon”, but they are not actually needed. In other words: if you pick up weapons of enemies you might get the trophy / achievement earlier, but it’s totally optional and not needed. To get “Full arsenal” you must get all of the Dog Tags & Hidden Weapons.
The Hidden Weapons can also be used in the Campaign after you find them. Some can even be used in Multiplayer! The Dog Tags can also be used in Multiplayer, so collecting everything gives you actual in-game content, rather than just a few new trophies or achievements.
MISSION 1: BAKU
MISSION 2: SHANGHAI
MISSION 3: SOUTH CHINA SEA
MISSION 4: SINGAPORE
MISSION 5: KUNLUN MOUNTAINS
MISSION 6: TASHGAR
MISSION 7: SUEZ