One more to add..
The engieers report of the siege of Spanish Fort in the O.R. mentions several times that there were two Whitworths placed to fire on Fort Huger and Tracy in late March/early April. later General Granger wrote to General Smith requisting his Whitworths be returned.
But I have two versions of the siege operations at Spanish Fort engineering maps. Both show one Whitworth, a Steel rifle, four parrotts, two 8 inch howitzers and two 100-pounder parrots placed on the south shore of Bay Minette to fire upon Fort Tracy and Fort Huger in action on April 8th. This is a reviewed map with General Canby's name, three engineers, and an inspector general of the engineer's department and is part of a report by the Chief Engineer submitted to Congress. They could be wrong.