What was the reason the shipbuilding program mandated by Second Vinson Act was created ?
With the additional displacement , the General Board was incredulous that a tonnage increase of would only allow the addition of s over the " South Dakota " s. Rather than retaining the 16 " / 45 caliber Mark 6 gun used in the " South Dakota " s , they ordered that future studies would have to include the more powerful ( but heavier ) 16 " / 50 caliber Mark 2 guns left over from the canceled s and battleships of the early 1920s .