American Battlefield Trust’s map of the Battle of Spotsylvania Court House on May 12, 1864, from 4am to 5am.
On the morning of May 12, 1864, the Union Army of the Potomac prepared to assault the Confederate Army of Northern Virginia positioned outside of Spotsylvania Court House, Virginia. Since May 5, the two armies had been locked in a titanic struggle—first in the Wilderness (May 5 & 6)—and now at Spotsylvania. On May 10, a Union assault broke through the Confederate fortifications. This attack on an area known as Doles Salient utilized a compact assault column on a narrow front, rather than a wide and shallow attack formation. Because of the success at Doles Salient, General Ulysses S. Grant ordered a major assault on the Confederate lines, utilizing a similar formation. Rather than utilizing an oversized brigade, Grant would employ an entire infantry corps. Grant intended to employ the 100,000 soldiers under his command to apply pressure along the Confederate lines so that the Rebels could not aid threatened portions of the lines, and in theory, the line would break under the sustained weight of the assault.
Near 4:35 am, some 20,000 men of the Federal II Corps stepped off toward the enemy position as dawn broke across the fields. The II Corps was deployed in a compact formation, and aimed for the tip of what the Confederates dubbed the "Mule Shoe." The Mule Shoe was a salient in the Confederate line that jutted dramatically northward toward the enemy—which exposed the defenders to attacks from three sides and converging artillery fire—while diluting the effectiveness of the defender's fire. It was a potentially fatal flaw that Maj. Gen. Winfield Scott Hancock and his corps exploited.
Hancock's men crashed into the main Confederate line around 4:50 am, initiating a 22-hour long battle. Union soldiers captured more than 3,000 Confederates, 20 cannons, and two general officers in the first hour of battle. More Federal soldiers attacked the eastern side of the salient. Commanded by Maj. Gen. Ambrose E. Burnside, the Union IX Corps waded the swamps and claimed rolling hills as it lent support to Hancock's men. But Grant's plan unraveled, as the western side of the salient was not attacked by the Union V Corps as ordered. Thus, Confederate General Robert E. Lee had a free hand to shift unengaged troops to the crisis point. Lee, too, ordered a new line one mile south of the Mule Shoe built to seal off the salient. But to accomplish this feat, Lee traded lives for time, and over the next 22-hours, Lee's men worked to hold their endangered line and thrust back the Federals who created a hole half-mile deep, and three-quarters of a mile wide in their lines.