DLC Vietnam: Complete the game in Survivor Mode (Host only).
Once you have completed Hours of Darkness, you will unlock Survivor Mode. In the Main Menu, launch the add-on and select this difficulty. Survivor Mode severely limits your resources and the number of weapons you can carry.
There is no set strategy for this mode, but one major tip is to take the time to rescue one or two of the US POWs; their firepower and general support during the final battle at the extraction zone will prove extremely advantageous. Also, it should go without saying that you should opt for stealth whenever possible and avoid secondary objectives altogether. Your main focus should be on getting to the extraction zone while remaining hidden in the dense jungle foliage.
Regardless of how you approach this mode, the achievement will unlock once you escape the jungle and the credits begin to roll.