Unlock: Liberate the Valsa Docks outpost.
Upon accepting this mission, Tang hires you to go grab three dog tags off of the corpses of Japanese soldiers in the area. The first is on an anti-aircraft cannon north of the quest giver, the second is on the cannon just east of the Valsa Docks, and the third is inside a well-hidden underground bunker southeast from the second tag’s location. There’s a red loot box near the third tag.
The later in the game you do this quest, the easier it’ll be. If you don’t run into any tricky random encounters along the way (this quest does take you into hills that tend to have a high chance of leopard attack), this is ten minutes’ work at most.