* This achievement is story related and can't be missed *
In the very first level you play you will be enlisted in to army, just walk right in to the building and continue right through it.... (my video below takes over from here)....just follow the button prompts to climb barriers and defeat the dummy soldiers.
Please note there are 2 collectables that I didn't pick up.......the first is the German soldiers helmet that is dropped when destroying the 2nd straw soldier that is hanging from the posts in basic training (watch for a shimmer to items that can be picked up).....the second is to the right of the flag pole on the ground, pick up before raising flag as can't be done afterwards.