High Quality Content by WIKIPEDIA articles! The 16"/45 caliber Mark 6 gun was a naval gun designed in 1936 by the United States Navy for their Treaty battleships. It was first introduced in 1941 aboard their North Carolina-class battleships, replacing the originally intended 14"/50 caliber Mark B guns and was also used for the followup South Dakota class. These battleships carried nine guns in three triple turrets. The gun was an improvement to the 16"/45 caliber guns used aboard the Colorado class, and the predecessor to the 16"/50 caliber Mark 7 gun used aboard the Iowa class.