What is the motivation of having heavy infantry to the right and light infantry to the left flank?

Question

In Napoleonic wars era, a line contains mostly regular troops except for two kind of elite units, the heavy one, e.g. grenadiers, they normally are the bravest, strongest troops with the best stamina, suitable for shock troops which is posted to the right, and the light one who are normally the best shooters/skirmishers, normally posted in the left flank.

What is the advantage or the motivation of this particular arrangement? I could somehow understand why the best units are posted at flanks , possibly to allow or guard against flanking attacks, but why is there preference to post best storm troops to the right and best shooters to the left (as opposed to the other way around, or have it symmetrical)?

Answer 1

This was an expression of the "traditional" order of fighting, elite troops, in the position of order on the right; lesser troops on the left.

The battle of Leuctra cited in another answer was an exception. But many military dispositions were not so rational. In the battle of Camden in the American Revolution, the British-trained American general, Horatio Gates was criticized by Alexander Hamilton for using this model. Hamilton opined that the best defensive ground was to the American right, and should have protected the worst troops, and the best attacking ground was to the left, better for America's elite troops.

Answer 2

This is basically oblique order. The idea is to crush one flank of the enemy with the strong force, turn it 90° and defeat the enemy in detail. The remainder of your troops keep the enemy busy on the other flank.

You put your heavy troops on the strong flank because they need the most strength (they need to break the line). The light troops are more useful for skirmishing. Their job here is to keep the enemy occupied. If the enemy penetrates your skirmishers, it is all over for your army. If the enemy realizes that your army is employing this tactic too soon, they will all fall on the strong flank and it will be crushed.

This technique was first used in Greece in the third century BC, but was most famously used by Frederick II of Prussia. Napoleon greatly admired Frederick II, and it is more than conceivable that Napoleon developed these tactics directly from him.

Answer 3

In the French Army of Napoleon size was not the critical qualifier for being a grenadier - experience and bravery was. Certainly diminutive size would disqualify a soldier from being eligible for the grenadier company of his battalion (but in turn making him eligible for the voltigeur company), but average size was sufficient (and a moustache was de rigeur).

Further, the internal layout of particular battalions was irrelevant for any battle larger than brigade on brigade, which virtually all Napoleonic battles were.

However, the martialing of troops onto the battlefield had long been done by having each unit send guides to mark out the right hand end of its intended deployment. Why the right hand end/side of the unit was chosen was simply traditional, and continued because everyone else did it, and all the drill manuals assumed it. However guides were sent to only one end/side of the unit because if the soldiers had to keep turning their heads to follow two sets of guides, this was certain to disrupt the unit as soldiers swung their heads from side to side and stepped on each other's heels.

Now, given that the guides were on the right hand end/side of the unit, and every soldier's eyes were angled right to follow the guides, where is the most correct and conspicuous place to put your most experienced troops, on whom all other eyes would be set? The right hand side of the unit. Hence the reason for placing the grenadiers, the bravest and most experienced men of the unit, on the right hand side as a model for all the rest of the battalion to emulate; the true place of honour.

The second elite company of the battalion, the voltigeurs, were designated to occupy the left hand end of the unit because they were in practice almost never there. In almost all circumstances they were detached as skirmishers either in front of, or to both flanks of, the battalion.