After Grant's army slipped past Lee's army to cross the James River, Hancock found himself in a position from which he might have ended the war. His corps arrived to support William Farrar Smith's assaults on the lightly held Petersburg defensive lines, but he deferred to Smith's advice because Smith knew the ground and had been on the field all day, and no significant assaults were made before the Confederate lines were reinforced. One of the great opportunities of the war was lost. After his corps participated in the assaults at Deep Bottom, Hancock was promoted to brigadier general in the regular army, effective August 12, 1864.