See subject. They certainly do a lot of shouting, and in the clips I’ve seen they are hoarse, and seem borderline unable to work as a DI for much longer.
(1992)
They didn’t shout nearly as much as film would have you believe.
They weren’t as grumpy either…usually.
Volume is produced from lots of diaphragm–that part is trained–They’re basically singing opera in an aggressive voice.
Never heard one lose his voice or go hoarse.
Certainly Marine Corps DI’s are taught to “carry” themselves in a certain fashion, to include how to “instruct” recruits. BTW, Lee Ermey’s performance as a mid/late 1960’s DI was spot on. Very different today, however.
My experience in Army boot camp/Infantry school (1993) was just the opposite. If anything, the DS’s screamed and cussed MORE than they do in the movies. There was even a bit of physical abuse, which isn’t supposed to happen anymore. Right. :rolleyes:
But there’s a LOT of variation in the platoons, companies, and training battalions even within one branch of the services, and certainly between branches themselves. Even in the same platoon, there was a wide degree of personality and behavior differences in our DS’s. (But most of them still screamed a lot. 
)
It’s no different that actors on stage - projection.
I went to the Ft. Benning Drill Sergeant School in 1998 and my voice developed a lot over the 9 weeks I was there. We marched, singing cadence everywhere we went. PT was conducted very loudly and we were expected to yell and scream aggressively. We were tested on the presentation of drill and ceremony classes (among others) and those classes were conducted outdoors and had to be heard from a distance.
I got hoarse very quickly, but then I got better and louder as the course went on. After that it was just a matter of keeping my voice in form. I used to claim that I was that loudest thing on two feet in that county.
I know for a fact that I couldn’t sing cadence or project my voice like that these days without paying for it.
The one main difference I’ve noticed between Army Drill Sergeants and Marine Drill Instructors is that Marines scream and get hoarse. Seems like their DI’s spend the entire cycle hoarse. Even the recruits can barely speak from all the screaming. I watched a Discovery Channel miniseries of Marine Boot Camp and everyone was hoarse the entire show, every episode.
I have to say that listening to those DI’s speak–and especially try to yell–was very annoying. Pretty much every Youtube clip I see of a DI has him yelling with a hoarse voice. I can’t stand the way they sound.
Army Drill Sergeants don’t scream. It doesn’t come from the back of the throat. It comes from the diaphragm as Inigo points out. This allows the person to yell all day without going hoarse.
I have heard that opera soloists temporarily lose visual acuity at high notes due to the pressure transferred from diaphragm to head voice. IIRC, the way I heard it is that they can’t wear contacts.
Often heard DI’s get hemorrhoids from all the shouting and tension.
Seriously, is there any truth in that?
My mother used to work at the PX at MCRD in San Diego, and she told me the DIs would be in 2-3 times a day buying throat lozenges.