The Confederate Army of the Potomac, whose name was short-lived, was the command under Brig. Gen. P.G.T. Beauregard in the early days of the American Civil War. Its only major combat action was the First Battle of Bull Run. Afterwards, the Army of the Shenandoah was merged into the Army of the Potomac with Gen. Joseph E. Johnston, the commander of the Shenandoah, taking command. The Army of the Potomac was renamed the Army of Northern Virginia on March 14, 1862, with Beauregard's original army eventually becoming the First Corps, Army of Northern Virginia.