John Ewen was a brigadier general in New York State's National Guard during the Civil War. When the Confederate Army of Northern Virginia invaded Pennsylvania, Ewen and his three regiments were sent to reinforce the Union troops, despite a War Department policy prohibiting state militia officers above the rank of colonel from fighting in the U.S. Army. At Gettysburg, his troops operated on the flanks of the enemy, but were not directly involved in the battle. After the Union victory, Ewen and his forces returned home on July 20, 1863. He later was elected as Comptroller of the City of New York.