Leave it to the Army. :rolleyes:
These U.S. Regulars at the time of the War of 1812 have the strap under the chin: http://www.thetroubleshooters.com/comet/1812war022_image002.jpg
Likewise this Louisiana militia officer, 1841: http://www.washingtonartillery.com/uniform%20Native%20American%201841%20litho.JPG
And these 1857 New York militiamen: Photo and Video Storage | Photobucket
And these pre-Civil War New Jersey troops: http://www.ng.mil/Images1/today/1228.jpg
And this Civil War regimental musician: http://thecivilwarimageshop.com/images/pict5161.jpg
But not, on the other hand, this 1823 New York militiaman: http://s2.hubimg.com/u/1903201_f260.jpg
Another wag: something about emphasizing big, manly chins?
And here are present-day U.S. Marines in summer dress uniform, with the straps under the chin: http://www.beardface.com/files/news_images/marine_dress_blues.jpg
There is a legend that the West Point uniforms date back to those worn by the first U.S. professional Army during the War of 1812. Also apocryphal, but still wonderful, is the comment supposedly made by the British commander who realized he was not facing a militia unit - “Those are regulars, by God!” The military equivalent of “you’re gonna need a bigger boat.”
There already is a word that means “lip strap”:
Gag.
As shown in the first link of post 42.
I doubt that this graduate knows the real answer. Is anyone interested enough to call the USMA directly and ask?
There’s Python for every occasion
http://www.montypython.net/scripts/nationwide.php
Better than holding up the lower lip. IMO that looks really stupid.
The tradition part, I understand.
I dunno about that. I always thought the Marine uniforms were a bit gaudy and looked like members of a parade or something. Just way over the top to be walking around in.
But, I’m ex-Navy so… my second favorite uniform was the now-discontinued Summer Working Whites… Yeah, the all white polyester material could be a pain in the ass to keep clean but you learn to adapt. Although, with a a garrison cap on I could have been either a milkman or waiter at a 50’s era diner. 
They still looked good and you stood out but it wasn’t over the top insane.
My 1st favorite? Dress Blues. Certainly the most “unique” of the US military.
I hated the old Sears mechanic style utilities. Incredibly dumb and pointless. Coveralls all the way.
The chin strap is used to keep the hat on, you know wind, horse riding, it is worn under the nose, mouth to keep the hat from being used on a sentry on duty to take him out. One kill method is to come up from behind reach over the hat grabbing preferable the bill and using it to break the neck by having a forearm position across the back of the senty and pulling straight back. If the hat is a tall one like one of those fur ones you might get more leverage out it. Many of these are very tall. If under the chin you have a major problem. If you have it postion under the nose, mouth, in the mouth the hat will give way. During WW I and WW II when they used those metal combat helmets with those wide metal brims all the way around those chin strap were left undone to prevent the blast pressure from catching those brims and breaking your neck or removing your head. The German WW II helmet is a much better design, it will not catch the blast, it was also a very difficult helmet to manufacture, more expense, and at one time the Allies were unsure of the process that was used to make them. Look at a modern Army combat helmet you can tell it is a knock off of the German WW II helment. A lot of military stuff makes sense, most was evolution via of quickly fixing design flaws. In modern metal helmets it was to install straps that would break or come loose at a given pressure.
Chin straps are to pacify the zombie soldiers of course.
This is fascinating. Cite?
I would think that that bit of knowledge would’ve made its way into wider knowledge by now, certainly with movies that go out of their way for historical accuracy.
Cites from memoirs?
I’m calling BS.
In the back of my head, I vaguely remember hearing this explanation. It would also make sense since the caps the cadets are wearing are rather tall which an attacker who approaches the soldier from behind could use to his advantage: the cap as a lever in connection with the chin strap are an ideal strangling device.
The answer to me is as simple as that as such get-ups passed from being practical workwear/fighting gear into merely ceremonial fancy dress, so some of their characteristics passed from being used as a practical component to just being used as a fancy accessory. Thus the underlip-strap. After all we don’t expect anyone to actually try a bayonet charge up a hill while wearing that.
I was among the last years of US troops going through basic with the M1 steelbucket helmet and the Drill Sergeants were, ahem, quite insistent that the chinstrap was to be always buckled and adjusted in proper form. Folks who let it dangle loose would get a loud and hearty, “Hey, who are you, John Wayne? You think those are there for style? Drop!”.
The WW1 helmet was meant to protect the soldier’s head from shrapnel from shell burst above the trench; the notion that shockwave would “catch” the helmet and yank your head off sounds like barracks myth spun by the old soldiers to confuse the new guys.
My guess is they’re showing off – they march round with such fine posture and grace that the lid doesn’t move. Maybe that was the Advanced Parade Marching class final - they had to do the drill sans chinstrap to pass. Then," hey let’s show everybody we can do it"! And the tradition was born.
What, they never heard of a quick release device?
And this:
really has me scratching my noggin.
mmm
If an enemy has managed to sneak up to grappling range without you noticing, then a strap under your nose isn’t going to save you.