A decisive attack, to be completely successful, must be followed up by fresh troops before the assaulting waves have been checked. Lee had crossed the Potomac and desired "to defeat the last army of the Federals in the east and drive the Northern Government from Washington." The battle of _Gettysburg_ lasted three days (July 1-3, 1863). On the first, the army of Northern Virginia was uniformly successful; on the second, the fortunes of battle swayed to and fro; on the third, Lee decided to make a Napoleonic decisive attack with half his available troops against Meade's centre. But the spirited attack of the first 15,000, after penetrating the line, was checked, and the remaining 15,000 did not arrive in support, so that the attack died down, was repulsed, and withdrew in disorder.
At _Chattanooga_ (November 25, 1868) Grant's decisive attack was successful, although delivered against a part of the position which appeared to be impregnable, on account of the strength of the attack, through { 62} distribution in depth; 25,000 men were hurled against the entrenchments in three lines, and the support of the third line carried the waves of the attack through the defences.
DETAILING THE UNITS.--The commander will detail the units for carrying out the Fire Attack, which will generally require one to three rifles per yard of the objective. This force will be placed under a definite commander, who will distribute it into a Forward Body to develop the attack in the firing line; Supports, to enable the Forward Body to assault the position; and Local Reserves to maintain or restore the advantages gained, their main function being to repel counter-attacks by similar bodies of the enemy and to maintain the offensive spirit.
The commander will also detail the units for carrying out the Decisive Attack, which will require three to five rifles per yard of the portion of the position against which it is projected. This force, under a definite commander, is distributed for the attack in depth, so that the strength and weight of the blow carries it home against all opposition. The force is retained by the commander of the whole attacking troops, to be thrown in at the right time and in the right place. It also remains in hand to restore the battle in case of an unexpected check, or to cover the withdrawal of the remainder of the troops if it is desired to break off the engagement.