On this date 150 years ago, the President and General McClellan discussed plans for the Army of the Potomac, and other military advisors concurred with McClellan's desire to enter Virginia by way of the peninsula southeast of Richmond. In "General War Order Number Two" the chief executive provided for certain of the Union troops to be positioned for defense of the Federal capital during the upcoming campaign, despite the fact that this would draw off troops from the offensive.

The Battle of Pea Ridge, Arkansas, the most significant of Civil War battles in the Trans-Mississippi west, saw the death of both Generals McCulloch and McIntosh, depriving the Confederacy of two able commanders. Federals under General Curtis continued to hold out for a second day of fighting, which ended when Van Dorn and his men retreated to the Arkansas River with orders to leave the state and head for the Mississippi River to aid in the defense of the Confederate position there. The tally of casualties showed that the Confederates had lost around 800 men, while the North suffered 1384 dead and wounded.

In Virginia at Hampton Roads, the ironclad "Merrimack" approached a squadron of Federal vessels, all much less well defended and ill-equipped to battle with the heavily armoured Confederate ship. In the ensuing encounter, two Union vessels are put out of commission - the USS "Cumberland" and the USS "Roanoke" - and the USS "Minnesota" was heavily damaged. Flag Officer Franklin Buchanan of the "Merrimack" was slightly wounded during the fight, though in general, few Confederates suffered serious injury. The Union forces suffered a greater number of casualties and damage to their ships was especially severe. Late in the day of the battle between the "Merrimack" and these various Federal vessels, the USS "Monitor" appeared in the harbor at Hampton Roads after a difficult journey south from New York.