About Vietnam Combat Jackets Question About U.S.Helmets In Some War Movies, Especially WW2 And Vietnam?

Question about U.S.Helmets in some war movies, especially WW2 and Vietnam? - about vietnam combat jackets

Hello I understood, often but not always, fighting for us soldiers during the fight without "taking over" chin strap. It is in every movie, and not every soldier is running, without the tape around the chin, but almost. Is it true to say, it was in the 2nd World War II and Vietnam in the common struggle, or is the invention of Hollywood?

Saving Private Ryan
http://www.youtube.com/watch?v=K0WBZab8S ...

bob
http://www.youtube.com/watch?v=xIgFNR7ZO ...

Bob landing - Note: Before you jump all the jugular, but after landing anymore?
http://www.youtube.com/watch?v=6IrB68Xs4 ...

The Thin Red Line
http://www.youtube.com/watch?v=LCmlOhsIw ...

longest day
http://www.youtube.com/watch?v=2NOFPtmox ...

WeSoldiers-Final Battle Scene
http://www.youtube.com/watch?v=ZPr9g3EVz ...

Hamburger Hill
http://www.youtube.com/watch?v=JDxnGHQNg ...

Full Metal Jacket
http://www.youtube.com/watch?v=TSRVLle4M ...

Can someone please explain? I am curious and ask.

As not all of WW2 and Vietnam film, and not all soldiers are running around saying, but only with their helmets from the leash, but for the most part.