Siege of Yorktown opens the Peninsula Campaign

Background. The Peninsula Campaign was a major Union operation in southeastern Virginia from March to July 1862. McClellan initially planned to transport the Army of the Potomac by ship to Urbanna to outflank Confederate forces near Washington. However, the emergence of the Confederate ironclad CSS Virginia and the Battle of Hampton Roads in March 1862 disrupted this plan, leading to operations focused on the Virginia Peninsula and Fort Monroe.

Confederate Defenses. Confederate General John B. Magruder commanded the Army of the Peninsula in April and May 1862, a period described as his greatest contribution to the Confederacy. In the winter of 1861, at Magruder's instruction, an earthen redoubt named Fort Magruder was constructed in front of Williamsburg, at the junction of the Yorktown and Lee's Mill roads — a defensive position on the Peninsula approach rather than at Yorktown itself. Magruder's initial line of defense was breached on April 4, but his more effective Warwick Line halted Union advances the following day.

Union Command. George B. McClellan organized and led the Union Army in the Peninsula Campaign from March through July 1862. He had been Commanding General of the United States Army from November 1861 to March 1862. His army disembarked for Fort Monroe from Alexandria and Annapolis on March 17, 1862, as part of the campaign's logistical preparations.