General-in-Chief at the outbreak of the war was the elderly Winfield Scott, who would clearly have to retire before long.
Although too old for any kind of active role, he was one of the few officers on either side who realized that it would be a long war, and his original plan - derided for its slowness - was more-or-less than plan that the Union eventually followed.
Commander of Union troops in the first pitched battle was the unfortunate Irvin McDowell, who knew his army was not ready for combat, but was pushed into it by politicians and press, hungry for action.
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That depends on which Union forces. U.S. Grant was overall commander of Union forces.
George Brinton McClellan
As army commander, U.S. Grant. He was reporting to the Union General-in-Chief, Henry Halleck.
Robert Anderson was the commanding officer for the Union during the Battle of Fort Sumter, and P. G. T. Beauregard was the Confederate commander. The battle resulted in a victory for the Confederacy.
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