Though deflection of the traditional round shot was the primary sloping rationale for ironclad designers, there actually was an added advantage involved, becoming more pertinent in the later stages of the war when armor penetrating ordnance was developed, especially by the Union Navy who at war's end had developed shells capable of penetrating up to 9 inches of perpendicularly placed armor hence the increase of armor thickness on Confederate ironclads Preston, 1979, p. 24 ; sloping increased effective armor thickness against armor piercing ordnance, which was typically fired on a flat trajectory.