High Quality Content by WIKIPEDIA articles! The armament of the Iowa-class battleships underwent a massive evolution since the first Iowa-class ship was laid down in June 1940. Owing to the continual evolution of the weaponry aboard these battleships they remain the most heavily armed gunships the United States has ever put to sea. In their World War II configuration, each of the Iowa-class battleships had a main battery of 16-inch (406 mm) guns that could hit targets nearly 20 statute miles (32 km) away with a variety of artillery shells designed for anti-ship or bombardment work. The secondary battery of 5-inch (127 mm) guns could hit targets nearly 9 statute miles (14 km) away with solid projectiles or proximity fuzed shells, and were equally adept in an anti-aircraft role and for damaging smaller ships. Each of the four battleships carried a wide array of 20 mm and 40 mm anti-aircraft guns for defense against enemy aircraft.