The first intel item is located once you reach the first objective of the game, when it asks you to "Locate the Beacon". Once you reach the beacon, your team mate will begin to use it. From it's location turn around 180 degrees, and head towards the humvee with a map pinned to it's side. Pick up this intel, and you will unlock this achievement.
View these videos for more intel locations:
Part 1:Part 2:Part 3: