[funkychinaman]

I'm not sure it's all Hollywood, if you look at archival footage from WWII to Vietnam, soldiers just let their straps dangle. The traditional answer was that soldiers didn't do it because supposedly, there was a danger that the concussion from a nearby explosion could break their necks. I think it's all a myth though because A) all the footage of our troops in Iraq and Afghanistan have their helmets securely strapped on, and it's not like explosions are no longer a danger on a modern battlefield, and B) you'd think that any concussion that can move a helmet so quickly it'd snap someone's neck would just outright kill him anyway.

I think it's just an American thing. All the old pictures of Bundewehr troops with the old M1 steel pot that I've seen had them strapped on, and all of the pictures of my dad from his ROC army days had him with an M1 strapped on too.