 Dual-purpose guns, often abbreviated to DP guns, were originally designed as a secondary armament for large surface ships such as cruisers and battleships to complement their heavy main armaments.Later, such guns began to be added to smaller vessels as their primary gun armament, and with the progression of ship design away from heavy caliber guns, today nearly all main gun armaments are of dual-purpose nature.Most modern dual-purpose guns are in the 76 mm to 127 mm (3 inch to 5 inch) caliber range.