On September 14, 1862, Cumming's brigade came up quickly to support troops under Brig. Gen. Howell Cobb, forced back from Crampton's Gap by a Federal offensive. His promptness helped keep the Union advance from its objective, Harpers Ferry. He was awarded a brigadier general's star six weeks later. Afterward, Cumming went west: first to Mobile, then in April 1863 to Mississippi as a subordinate to Lt. Gen. John C. Pemberton. He led a brigade in Maj. Gen. Carter L. Stevenson's division at Champion's Hill and in the actions outside Vicksburg. Captured and paroled with the city's garrison, he reorganized Stevenson's old brigade at Decatur, Georgia, in the fall of 1863 and led it gallantly at Missionary Ridge.