This subject came up in the Chief of Staff thread, and it seemed a good idea (or not) to start a new thread on this subject. Zack put a question on the subject which I believe deserves its own thread.
'As an organisational unit the corps (or at least the self reliant division which could hold its own until assistance arrived) dated back to Bourcet and his work published in 1775. (Mike Rapport, The Napoleonic Wars, p60). What was changed in 1800?'
First, some definitions:
From: A Military Dictionary, or Explanation of the Several Systems of Discipline of Different Kinds of Troops, Infantry, Artillery, and Cavalry by William Duane (1810):
Corps: And body of forces, destined to act together under one commander-106,
From: Military Dictionary: Comprising Terms, Scientific and Otherwise, Connected with the Science of War by GE Doyle (1876):
Corps: Any body of forces destined to act together under one commander. The terms is commonly made use of by military writers in speaking or writing of an army corps.-93.
Corps d'armee: Army corps. One of the sub-divisions, and the first unit of a large army.-93
Division of an Army: First unit of a corps d'armee, and commanded by a general officer. It consists of two or more brigades, composed of the three arms of the service.-112.
From: Definitions and Doctrine of the Military Art by John Alger:
Corps: 'After 1804, the smallest force of all arms in the French Army was the corps, which was generally commanded by a marshal and consisted of two to four infantry divisions, a brigade or division of light cavalry, and a company or two of artillery, engineers, and service units. None of Napoleon's corps or divisions had a standard organization. The size and composition of each depended upon the capabilities of the commanders, the strategic situation, and the available troops.'-64.
Division: 'The division was composed of two or more brigades or regiments. The term division did not appear until the late eighteenth century, although there was a less formal and more general use of the word to denote a division, or simply a part, of any larger organization.'-46.
From: Swords Around a Throne by John Elting:
Brigade: two or more regiments.-57.
Division: two or more brigades.-57
Corps d'armee (army corps): 'This is the equivalent of the modern corps.'-58, 685 note 10.
It should also be noted that the term 'corps' was also used to designate or denote certain units and had nothing to do with a corps d'armee.
The French under de Broglie (whose chief of staff was Pierre Bourcet) began forming ad hoc divisions at the end of the Seven Years War and in March 1776, based on de Broglie's work, Saint-Germain 'officially established divisions.' France was divided into military departments, and the troops stationed in each department formed a division. These were not uniform but were composed of three to seven brigades, a mix of infantry and cavalry, sometimes only of infantry or cavalry, and no artillery was usually assigned.
When war came in 1792 the military divisions were territorial commands. For field service, separate divisions of all arms (infantry, cavalry, and artillery) were formed and divisions were then assigned to the field armies. These divisions were then temporarily assigned to the field armies and grouped temporarily into ad hoc 'groupings' that were designated as 'left wing', 'center', 'right wing' and sometimes using additional ad hoc formations designated as 'reserve' or 'advance guard.'
Napoleon and Moreau (the latter at Napoleon's direction) formed their divisions into corps d'armee and these corps were to have permanent staffs (For Napoleon's directions to Moreau to form his army into four corps, see Napoleon's Correspondence, VI, Number 4694, page 201: Plan de campagne pour l'armee du Rhin, dated 22 March 1800). Napoleon formed the Armee de la Reserve into corps d'armee, each having infantry divisions assigned to them, corps troops (gendarmes, administrative personnel, engineers, and artillery). The majority of the cavalry was formed into a reserve under Murat (see Gaspar du Cugnac, Campagne de l'Armee de Reserve in 1800, and its English translation by Conrad Lanza, Marengo Campaign, 1800: Source Book).
The corps d'armee, or usually termed a corps, was a headquarters with assigned corps troops (artillery, engineers, gendarmerie, administrative personnel and a permanent staff) which was assigned from two to five infantry divisions and a brigade or a division of light cavalry. The strength assigned to them by Napoleon was not uniform, but was based on the corps' commanders ability and to confuse enemy intelligence. The system was flexible, with divisions being able to 'move' from one corps to another depending on the situation. Further, additional corps were formed when necessary, such as Mortier's VIII Corps in 1805 and a Reserve Corps commanded by Lannes in both 1807 and 1809.
Desaix's corps in 1800 has been mentioned and a corps was formed to give him a command when he arrived in theater from Egypt from available assets. He did not have a staff with him, so Boudet's division staff was used instead. Even though the Armee de la Reserve was formed from various and diverse units as Napoleon was 'scraping the bottom of the manpower barrel' to form it and units were sent to Berthier who was organizing it for the movement across the Alps into northern Italy and across the Austrian line of communications.
The corps d'armee, or more simply, the corps, was developed/invented by Napoleon and greatly facilitated command and control. The idea that the Prussians developed it is incorrect-they copied it as common practice from the French as did the Austrians (along with staff organization and functioning, althouth neither 'caught up' during the period). Even in 1815 in Belgium Wellington organized the Anglo-Dutch army in corps, although these were administrative organizations, not combat organizations.
Napoleon initiated the employment of the corps in 1800 and institutionalized it in 1804-1805 in the Grande Armee. The French training camps along the Channel were redesignated as numbered corps when the Grande Armee was announced in August 1805 formed from the Armee des Cotes de l'Ocean on the Channel. It consisted of seven numbered Corps (I-VII), the Cavalry Reserve and the Imperial Guard.