The debate over what should follow the Collasuyu Class battleships raged far and wide and ended up with the Emperor having the final say. To keep the costs and building times down, as many parts and design of the Collasuyu class were passed through to the new Aconcagua class ships. The basic design was lengthened and the breadth reduced to improve the hull form. The bow was also altered to improve speed. More than twice the horsepower of the Collasuyu was required to make the design speed of 27 knots. To make these changes happen required a change of layout of the main armament, the 'Q' turret being remounted to a superfiring 'B' position. The space provided by the removal of 'Q' turret was filled with the extra propulsion systems.
The other way to assist the Aconcagua to achieve its speed recommendation was to lighten the ship. This entailed the removal of the 6" battery and the area being plated over, the space provided being used for extra coal stowage. The major change was the armoured belt being reduced from 13" to 10", and the deck armour being reduced from 3.5" to 2".
The final result was a 21,000 ton ship, 572 feet long, 82 feet wide, 60,000shp through 4 shafts for 27 knots. The armament was 8 x 12" (4x2), 12 x 100mm (12x1), 13 x 3pd (13x1).