FOR READERS UNFAMILIAR WITH MILITARY TERMINOLOGY, OR WITH the organization of Civil War armies, some brief definitions and descriptions may be useful.
CIVIL WAR MILITARY UNITS
The basic unit of Civil War military organization was the regiment, usually raised by state governments and recruited from a particular city or district. The initial strength of a regiment was 1,000–1,200 officers and men, but disease shrank that number before a unit reached the field, after which casualties and desertions took their toll. Veteran regiments in the Antietam campaign might number 150 or fewer, while “rookie” regiments mustered nearly a thousand. A regiment was supposed to be commanded by a colonel, but because of illness, wounds, or other causes, command often fell to lower-ranking officers.
A brigade is a group of four or five regiments, with an attached artillery battery. Brigades were supposed to be commanded by brigadier generals, and in the Confederate armies they generally were. But the Union was slow to grant general’s stars, so many Federal brigades were led by colonels. The Confederate army was more assiduous than the Federals about organizing brigades by state but was not always able to do so. Rebel brigades were known by the name of their commander (for example, Hood’s Brigade) or by an officially designated nickname (Stonewall Brigade). Union brigades were designated by number, though some earned unofficial nicknames: for example, the Iron Brigade and the Irish Brigade.
A division is a group of brigades. In the Antietam campaign, Confederate divisions ranged between four and six brigades, and were typically commanded by major generals; while Union divisions had three or four brigades and were commanded by colonels and brigadiers as well as major generals. Confederate divisions were named for their commanders; Union divisions were numbered.
A corps or army corps is a group of divisions. Two or more corps were sometimes combined to form a wing. During the Antietam campaign, the corps structure of Lee’s army was not yet firmly established. Although Generals Longstreet and Jackson had commanded groups of divisions for months before Antietam, Lee had often altered the composition of their commands in response to events. How and why he did so is part of the story that follows. However, Lee consistently followed the principle of corps command, which was to delegate control of large-scale tactical operations to a single trusted commander with the rank of lieutenant general. Union corps were smaller than Confederate corps and usually commanded by major generals. When Confederate corps were finally established, they would be named for their commanders, while Union corps were numbered.
An army is a group of corps. Until 1864, the Federal government refused to authorize any grade higher than major general. Hence Union armies were commanded by major generals, while Confederate armies were led by generals or “full generals.” Union armies were named after rivers, Southern armies after the territories they were initially assigned to defend. Thus McClellan’s force was called the Army of the Potomac, while Lee’s was the Army of Northern Virginia.
The basic artillery unit was the battery, consisting of four to six horse-drawn guns and their supporting equipment and ammunition, which was carried in wheeled limber-chests and supply wagons. Each battery was divided into two or more sections that might maneuver separately in action. Batteries were administratively organized into regiments and battalions, but in practice most were distributed to brigades and divisions as autonomous units. Lightweight, short-range batteries of smoothbore cannons (some called “Napoleons”) were attached to brigades for action with the infantry. Divisions, corps, and the army also disposed of artillery reserves, which included both smoothbores and longer-range pieces with rifled barrels, which fired heavier-weight shells. At long ranges (800–1,800 yards), guns fired solid shot or explosive shells of various sizes, which were effective against infantry and enemy batteries. Exploding case-shot—a hollow shell packed with six large lead or iron balls—was used against infantry at ranges of 500 to 800 yards. The deadliest antipersonnel ammunition was canister, a cylinder of thin metal packed with 100–120 lead or iron balls bedded in sawdust. A cannon firing canister was like a giant shotgun, which was devastating at ranges up to 400 yards but could be effective up to 600 yards.
MILITARY TERMINOLOGY
Strategy is commonly used to describe large-scale military planning, from “grand strategy,” which may be international in scope, to the planning of an entire war, to the design of a military campaign for the conquest of a region or theater of operations. In this book,strategy refers to the planning of a war as a whole, in which the use of military force is systematically tied to ideas about the nation’s war aims—that is, the political objectives for which the war is being fought.
Operations are the actual movements planned or actually made by armies. A campaign is a series of operations designed to achieve a significant objective, such as the capture of a major city or the destruction of an opposing army. The region in which a campaign plays out is called a theater of operations. Tactics are the movements and actions of military units when in contact with the enemy.
Some of the operational and tactical maneuvers described in this book may require definition. Civil War armies fought in lines. The basic infantry weapon was the single-shot muzzle-loaded rifle-musket, and the only way to deliver massed fire on the battlefield was to form the infantry in two lines, one behind the other. The range and power of rifles and artillery were such that frontal assaults against strong battle lines were generally doomed to failure. If two hundred riflemen advance directly against another line of two hundred, the attackers have no advantage in firepower, and if they stop firing and attempt a charge they are at a disadvantage. The best way to break a battle line is to attack it from the flank, by finding a gap or open area, pushing troops through it, and wheeling one’s battle line to face the end of the enemy’s line—as if crossing the top of a capital “T.” Now, instead of fronting an equal number of riflemen, the attacker faces only two defenders; and his own fire enfilades the defender’s line—rips down it from end to end. Since the attacker’s line is wider than the defender’s flank, the attacker also threatens to hit the enemy unit from the rear or cut it off from the rest of its army. The defenders have little choice but to retreat, or break and run.
That same principle of the flanking maneuver applies to the movement of armies. An army’s defensive position inevitably took the form of an extended line, to defend its lines of supply and to bring its firepower into play. To drive an army from its position without attacking frontally, an attacker had to turn the defender’s flank. By making a turning maneuver around the end of the defender’s line, the attacker could reach a position from which he could either attack the endmost unit of the defending army, and “roll up” the line by striking each unit in turn from end to end; or strike at the defender’s line of supply, cutting him off from food and ammunition and compelling him to retreat.