Peninsula Campaign - Opposing Forces

Opposing Forces

Further information: Confederate order of battle, Union order of battle

Union corps commanders
Brig. Gen. Edwin V. Sumner Brig. Gen. Samuel P. Heintzelman Brig. Gen. Erasmus D. Keyes

The Army of the Potomac had approximately 50,000 men at Fort Monroe when McClellan arrived, but this number grew to 121,500 before hostilities began. The army was organized into three corps and other units, as follows:

• II Corps, Brig. Gen. Edwin V. Sumner commanding: divisions of Brig. Gens. Israel B. Richardson and John Sedgwick
• III Corps, Brig. Gen. Samuel P. Heintzelman commanding: divisions of Brig. Gens. Fitz John Porter, Joseph Hooker, and Charles S. Hamilton
• IV Corps, Brig. Gen. Erasmus D. Keyes commanding: divisions of Brig. Gens. Darius N. Couch, William F. "Baldy" Smith, and Silas Casey
• 1st Division of the I Corps, Brig. Gen. William B. Franklin commanding
• Reserve infantry commanded by Brig. Gen. George Sykes
• Cavalry commanded by Brig. Gen. George Stoneman
• The garrison of Fort Monroe, 12,000 men under Maj. Gen. John E. Wool; Wool was quickly transferred to another department for duty in Baltimore after the War Department realized that he technically outranked McClellan.

Confederate wing commanders
Maj. Gen. D. H. Hill Maj. Gen. James Longstreet Maj. Gen. John B. Magruder

On the Confederate side, Johnston's Army of Northern Virginia (newly named as of March 14) was organized into three wings, each composed of several brigades, as follows:

• Left Wing, Maj. Gen. D. H. Hill commanding: brigades of Brig. Gen. Robert E. Rodes, Winfield S. Featherston, Jubal A. Early, and Gabriel J. Raines
• Center Wing, Maj. Gen. James Longstreet commanding: brigades of Brig. Gens. A.P. Hill, Richard H. Anderson, George E. Pickett, Cadmus M. Wilcox, Raleigh E. Colston, and Roger A. Pryor
• Right Wing, Maj. Gen. John B. Magruder commanding: division of Brig. Gen. Lafayette McLaws (brigades of Brig. Gens. Paul J. Semmes, Richard Griffith, Joseph B. Kershaw, and Howell Cobb) and division of Brig. Gen. David R. Jones (brigades of Brig. Gens. Robert A. Toombs and George T. Anderson)
• Reserve force commanded by Maj. Gen. Gustavus W. Smith
• Cavalry commanded by Brig. Gen. J.E.B. Stuart

However, at the time the Army of the Potomac arrived, only Magruder's 11,000 men faced them on the Peninsula. The bulk of Johnston's force (43,000 men) were at Culpeper, 6,000 under Maj. Gen. Theophilus H. Holmes at Fredericksburg, and 9,000 under Maj. Gen. Benjamin Huger at Norfolk. In Richmond, General Robert E. Lee had returned from work on coastal fortifications in the Carolinas and on March 13 became the chief military adviser to Confederate President Jefferson Davis.

Forces in the Shenandoah Valley played an indirect role in the campaign. Approximately 50,000 men under Maj. Gens. Nathaniel P. Banks and Irvin McDowell were engaged chasing a much smaller force under Stonewall Jackson in the Valley Campaign. Jackson's expert maneuvering and tactical success in small battles kept the Union men from reinforcing McClellan, much to his dismay. He had planned to have 30,000 under McDowell to join him.

Magruder had prepared three defensive lines across the Peninsula. The first, about 12 miles (19 km) north of Fort Monroe, contained infantry outposts and artillery redoubts, but was insufficiently manned to prevent any Union advance. Its primary purpose was to shield information from the Union about a second line extending from Yorktown to Mulberry Island. This Warwick Line consisted of redoubts, rifle pits, and fortifications behind the Warwick River. By enlarging two dams on the river, the river was turned into a significant military obstacle in its own right. The third defensive line was a series of forts at Williamsburg, which waited unmanned for use by the army if it had to fall back from Yorktown.