On January 27, President Lincoln issued a war order authorizing the Union to launch a unified aggressive action against the Confederacy. General McClellan ignored the order.
On March 8, President Lincoln -- impatient with General McClellan's inactivity -- issued an order reorganizing the Army of Virginia and relieving McClellan of supreme command. McClellan was given command of the Army of the Potomac, and ordered to attack Richmond. This marked the beginning of the Peninsular Campaign.
In an attempt to reduce the North's great naval advantage, Confederate engineers converted a scuttled Union frigate, the U.S.S. Merrimac, into an iron-sided vessel rechristened the C.S.S. Virginia. On March 9, in the first naval engagement between ironclad ships, the Monitor fought the Virginia to a draw, but not before the Virginia had sunk two wooden Union warships off Norfolk, Virginia.
On April 6, Confederate forces attacked Union forces under General Ulysses S. Grant at Shiloh, Tennessee. By the end of the day, the federal troops were almost defeated. Yet, during the night, reinforcements arrived, and by the next morning the Union commanded the field. When Confederate forces retreated, the exhausted federal forces did not follow. Casualties were heavy -- 13,000 out of 63,000 Union soldiers died, and 11,000 of 40,000 Confederate troops were killed.
General Quincy A. Gillmore battered Fort Pulaski, the imposing masonry structure near the mouth of the Savannah River, into submission in less than two days, (April 10-11, 1862).
Flag Officer David Farragut led an assault up the Mississippi River. By April 25, he was in command of New Orleans.
In April, General McClellan's troops left northern Virginia to begin the Peninsular Campaign. By May 4, they occupied Yorktown, Virginia. At Williamsburg, Confederate forces prevented McClellan from meeting the main part of the Confederate army, and McClellan halted his troops, awaiting reinforcements.
Confederate General Thomas J. "Stonewall" Jackson, commanding forces in the Shenandoah Valley, attacked Union forces in late March, forcing them to retreat across the Potomac. As a result, Union troops were rushed to protect Washington, D.C.
On May 31, the Confederate army attacked federal forces at Seven Pines, almost defeating them; last-minute reinforcements saved the Union from a serious defeat. Confederate commander Joseph E. Johnston was severely wounded, and command of the Army of Northern Virginia fell to Robert E. Lee.
Between June 26 and July 2, Union and Confederate forces fought a series of battles: Mechanicsville (June 26-27), Gaines's Mill (June 27), Savage's Station (June 29), Frayser's Farm (June 30), and Malvern Hill (July 1). On July 2, the Confederates withdrew to Richmond, ending the Peninsular Campaign.
On July 11, Major-General Henry Halleck was named general-in-chief of the Union army.
Union General John Pope suffered defeated at the Second Battle of Bull Run on August 29-30. General Fitz-John Porter was held responsible for the defeat because he had failed to commit his troops to battle quickly enough; he was forced out of the army by 1863.
Union General McClellan defeated Confederate General Lee at South Mountain and Crampton's Gap in September, but did not move quickly enough to save Harper's Ferry, which fell to Confederate General Jackson on September 15, along with a great number of men and a large body of supplies.
On September 17, Confederate forces under General Lee were caught by General McClellan near Sharpsburg, Maryland. This battle proved to be the bloodiest day of the war; 2,108 Union soldiers were killed and 9,549 wounded -- 2,700 Confederates were killed and 9,029 wounded. The battle had no clear winner, but because General Lee withdrew to Virginia, McClellan was considered the victor. The battle convinced the British and French -- who were contemplating official recognition of the Confederacy -- to reserve action, and gave Lincoln the opportunity to announce his Preliminary Emancipation Proclamation (September 22), which would free all slaves in areas rebelling against the United States, effective January 1, 1863.
The Army of the Potomac remained in possession of the field, and the photographers were able to work over it thoroughly immediately after the battle of September 17. One can witness President Lincoln's visit to McClellan's headquarters, and follow the army across the Potomac at Berlin (present day Brunswick, Maryland) and into re-occupied Harper's Ferry.
General McClellan's slow movements, combined with General Lee's escape, and continued raiding by Confederate cavalry, dismayed many in the North. On November 7, Lincoln replaced McClellan with Major-General Ambrose E. Burnside. Burnside's forces were defeated in a series of attacks against entrenched Confederate forces at Fredericksburg, Virginia, and Burnside was replaced with General Joseph Hooker.