For Napoleon's Army it would be the Imperial Guard. This new unit was not only his personal bodyguard but also an army corps. Constituted of 9,775 soldiers at first, two thirds being veterans, the Imperial Guard was theoretically supposed to number a total of 126,850 infantrymen, cavalrymen, and gunners in 1815. As a matter of fact, it actually only had 17,498 in January of 1814, due to the losses of the Spanish and Russian campaigns.
These legionnaires were the shock troops of Napoleon's army. His tactics were based on the extreme mobility of his troops. By imposing long marches on his soldiers, he was able to achieve an effect of surprise on an unsuspecting enemy. "It is not with our arms, but with our legs that the Emperor beats the Austrians," remarked a soldier. To survive these extended marches, his soldiers had to be the best of the best, and they were.
To be admitted as a foot grenadier in the Imperial Guard a soldier had to have a height of at least 5 foot 5 inches, five years of service, have been distinguished on the moral as well as on the military point of view, and to have participated in at least two campaigns.
In general foot units designated as Grenadiers had, by the time of the Napoleonic Wars, ceased using the hand-thrown grenades, and were largely known for being composed of physically big men, frequently relied upon for shock actions.
Cavalry units designated as Battle Cavalry were all cavalry units that mounted large horses and were used to deliver a physical shock to either enemy cavalry or infantry. They were so called from the 18th century belief that they were the deciders of the battle, always kept as a final reserve to be used to break the enemy ranks.