When that very unique sound rolled across the parade ground everyone from the newest recruit to the oldest veteran scrambled to get into position in the formation. That sound could only have come from the Drill Sergeant--and you sure didn't want to attract his attention by doing something wrong.
He needed no electronic amplification of his voice for his command to be heard and understood. His was not the proper diction of polite society. He had a job to do and by god you weren't going to prevent him from doing it. Everyone on that parade ground belonged to him and they better all do exactly what they had been trained to do.
The common concept of military discipline is one of whippings, floggings and other in-your-face tactics that make people terrified to not do whatever they are ordered to do.
But the Corps of Discovery was different. Although we read of several instances of court martials and floggings, the Captains mainly used very different training methods than what had been the accepted norms [Read "Sea of Glory" by Nathaniel Philbrick to see the normal military command and discipline of that era. It is the story of Captain Charles Wilkes exploring voyage around the world in the years 1838-1842]
Lewis and Clark had a new and unique military mission to perform. Their mission has been favorably compared to current day special ops missions. Think of the best of the best. Think Navy Seals, Air Force Thunderbirds, Navy Blue Angels. These precision teams had to be able to totally rely upon each other and know that everyone knew and did their jobs; their was no time for questioning.
All training needs to have appropriate punishments for failures. Whippings and floggings were used when appropriate, but the Captains had other alternatives that they used more frequently. They were able to pick and choose depending upon the situation at had.
The Corps of Discovery became a team; a force of men that had learned they could fully depend on each other in any situation; a force of men that had leadership that employed sound management techniques; leadership that was an integral part of the teams that had been carefully developed.