...your obedient servant. B. M. Prentiss, Major-General, To David D. Porter, Rear-Admiral, Commanding Mississippi Squadron. Helena, Ark., July 12, 1863. At last we have been attacked by Missouri 's favorite general, under the direction of the laggard Holmes. At four o'clock A. M., on the fourth day of July, the siege-gun, which was to give the signal of attack, belched forth its startling a...