Keep shooting at it until it shoots rockets at you. Then it flys away for awhile. Then it comes back.
The helicopter person finally shoots the helicopter down. After that the gate door at the right side of thhe fence should open. Go through it and go to the building and kill all the guys and then survive waves of enemies then you finally kill Gabriel.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.