I understand that large armies would obviously have people ranked below the leader, but i was watching a YT video on Napoleon and was baffled at how he was able to control such a large army. In one war/battle Napoleon was leading his army through Russia with 600K soldiers, how on earth would he even be able to communicate his plans effectively to all of his soldiers? Would it just become a long game of telephone where soldiers would communicate the plan to other soldiers? I also understand that Napoleon liked to utilize smaller armies for better maneuverability, but still, we re talking about thousands of soldiers where the only way to communicate is through written letters and word of mouth. On top of the limited communication, I would also imagine that it would be a lot harder to communicate what your plan is in the midst of battle where a leader needs to quickly react to what the enemies are doing.
Sorry I'm late in answering this, but I think it's important to know that most soldiers, through most of history, weren't told of the grand battle plan. You were told where to go and what to do by your company commander, who was interpreting their orders from the battalion commander, who was interpreting their orders from the brigade commanders, and so on. The army commander had a plan, and would entrust part of its execution to their subordinates. Those subordinates, in turn, would command their subordinates to move their commands to accomplish their objectives. The common soldier doesn't need to know the grand battle plan- only what they need to do (it's a potential security risk for everyone to know your detailed battle plan!)
I'll give a few example from the American Revolutionary War: Here's an example from New England forces in Cambridge's General Orders, July 8th, 1775:
"Ordered that the main guard on no Account whatever, be without a Drum, which is to beat to Arms on any Alarm and be followed by all the drums in the Camp; On which every Officer and Soldier is immediately to repair to the Alarm post.
The Commanding Officer of each Regiment or Corps in Cambridge as soon as the Men are paraded after an Alarm, to send an Officer to Head Quarters for orders.
The commanding Officers at Roxbury, Prospect hill Winter-hill and Sewalls point to send Expresses in case of Alarm to Head Quarters with an account of the Situation and the movements of the enemy—If they are not each provided with a Horse for that purpose; the Adjutant General to apply to the Committee of supplies..."
Notice that it's the general officers that are going to get orders. They would relay their orders to their respective regiments or corps.
Later in the war, you can get a picture of the officers Washington would relay his commands to directly in the minutes of the Councils of War he had to discuss issues and get the opinions of his officers. Here's one from September 23rd, 1777:
"[Camp near Pottsgrove, Pa., 23 September 1777]
At a Council of War held at the Camp near Potts Grove the 23d day of Septemr 1777.
Present His Excellency the Commander[,] Major Generals Sullivan[,] Green[,] Lord Stirling[,] Stephen[,] Armstrong[,] Brigadiers General Knox[,] Weedon[,] Nash[,] Scott[,] Conway[,] Potter.
Besides the above Major Genl St Clair and John Cadwolader Esquire were also present.
His Excellency informed the General Officers that the Reason of his calling them together was to acquaint them that the Enemy had, the preceeding night, crossed the Schuylkill by several Fords about twelve Miles below and by the best accounts were proceeding towards Philadelphia.1 He also informed them that the Troops under Generals Smallwood & Wayne had not yet rejoined the Army and that a Brigade of Continental Troops under the command of General Mcdougal might be expected in a few days from Peekskill and about one thousand Militia from Jersey under Genl Dickinson in the same time..."
As you can see, the direct orders and discussions were going to the divisional and brigade commanders. They would separately draw up orders for their brigades and regiments.
So, how were these orders transmitted? Often times orally, in person, as in the Councils of War. These could also be delivered in written form, as here George Washington's commands to Brig. Gen. James Ewing on Dec. 12th, 1776:
"Orders to Brigadier General James Ewing
[Trenton Falls, 12 December 1776]Sir
Your Brigade is to guard the River Delaware from the Ferry opposite to Burdentown till you come within two miles or thereabouts of Yardly’s Mill, to which General Dickenson’s command will extend.1
About One hundred, or a hundred and fifty Men will I should think, be sufficient at the Post opposite to Burden Town—the principal part of your Force should be as convenient as possible to the ford above Hoops’s Mill,2 in order that if a passage should be attempted at that place, you may give the earliest and most spirited opposition, the success of which depending upon good intelligence and the vigilance of your Guards and sentries, will induce you to use every means in your power to procure the first and every endeavour to enforce & encourage the latter.
Between Burdentown and the Mill, and from the Mill to the extent of your Line above, you are to have intermediate Guards and Centries, who are to be as attentive as possible in discovering, and informing you of every movement of the Enemy—constant patroles are also to pass—In a word, so much depends upon watchfullness that you cannot possibly be too much upon your Guard.
As the Ford from the Jersey Shore leads on to the upper end of the Island adjoining the Mill, you are to throw up a breast Work for Musquetry near the landing place, and secure your communication with it—Besides this work another on the height on this Side for a Field Piece or two should be erected..."
As you can see, pretty detailed, no? That's what many written orders would look like.
In battle, orders would often be relayed orally by adjutants- that was one of their primary jobs in battle. Also, this is why field officers (those responsible for brigades and larger formation) were mounted on horses- they had to get around the battlefield quickly. One of the most famous instances of this when Washington rode over to confront General Lee as his forces retreated at the Battle of Monmouth.
Works cited:
“Council of War, 23 September 1777,” Founders Online, National Archives, https://founders.archives.gov/documents/Washington/03-11-02-0305. [Original source: The Papers of George Washington, Revolutionary War Series, vol. 11, 19 August 1777 – 25 October 1777, ed. Philander D. Chase and Edward G. Lengel. Charlottesville: University Press of Virginia, 2001, pp. 294–298.]
“From George Washington to Colonel John Cadwalader, 11 December 1776,” Founders Online, National Archives, https://founders.archives.gov/documents/Washington/03-07-02-0230. [Original source: The Papers of George Washington, Revolutionary War Series, vol. 7, 21 October 1776–5 January 1777, ed. Philander D. Chase. Charlottesville: University Press of Virginia, 1997, p. 294.]
“General Orders, 8 July 1775,” Founders Online, National Archives, https://founders.archives.gov/documents/Washington/03-01-02-0041. [Original source: The Papers of George Washington, Revolutionary War Series, vol. 1, 16 June 1775 – 15 September 1775, ed. Philander D. Chase. Charlottesville: University Press of Virginia, 1985, pp. 75–77.]