In the first days of the Revolution our troops, undrilled and not strictly disciplined, could not fight in line. To advance on the enemy, a part of the battalion was detached as skirmishers. The remainder marched into battle and was engaged without keeping ranks. The combat was sustained by groups fighting without formal order. The art was to support by reserves the troops advanced as skirmishers. The skirmishers always began the action, when indeed they did not complete it.
To oppose fire by rank to skirmishers was fools' play.
Skirmishers necessarily opposed each other. Once this method was adopted, they were supported, reinforced by troops in formation. In the midst of general firing fire at command became impossible and was replaced by fire at will.
Dumouriez, at the battle of Jemmapes, threw out whole battalions as skirmishers, and supporting them by light cavalry, did wonders with them. They surrounded the Austrian redoubts and rained on the cannoneers a hail of bullets so violent that they abandoned their pieces.
The Austrians, astounded by this novel combat method, vainly reinforced their light troops by detachments of heavy infantry. Their skirmishers could not resist our numbers and impetuosity, and presently their line, beaten by a storm of bullets, was forced back. The noise of battle, the firing, increased; the defeated troops, hearing commands no longer, threw down their arms and fled in disorder.
So fire in line, heavy as it may be, cannot prevail against the power of numerous detachments of skirmishers. A rain of bullets directed aimlessly is impotent against isolated men profiting by the slightest cover to escape the fire of their adversaries, while the deployed battalions offer to their rifles a huge and relatively harmless target. The dense line, apparently so strong, withers under the deadly effect of the fire of isolated groups, so feeble in appearance. (General Renard.)
The Prussians suffered in the same way at Jena. Their lines tried fire at command against our skirmishers. You might as well fire on a handful of fleas.
They tell us of the English salvos at Sainte-Euphémie, in Calabria, and later in Spain. In these particular cases they could be used, because our troops charged without first sending out skirmishers.
The battle of Sainte-Euphémie only lasted half an hour; it was badly conceived and executed, "And if," says General Duhesme, "the advancing battalions had been preceded by detachments of skirmishers who had already made holes in enemy ranks, and, on close approach, the heads of columns had been launched in a charge, the English line would not have conserved that coolness which made their fire so effective and accurate. Certainly it would not have waited so long to loose its fire, if it had been vigorously harassed by skirmishers."
An English author, treating of the history of weapons, speaks of the rolling fire, well directed, of the English troops. He makes no mention of salvos. Perhaps we were mistaken, and in our accounts have taken the fire of a battalion for the formal battalion fire at command of our regulations.