Main armament of US battleships South Carolina and Michigan were 30,5cm/12” guns according to the Dutch magazine Marineblad dated 1905-1906 no. 5

An item referred to the Army and Navy Journal reported that the American battleships South Carolina and Michigan now being designed were to armed with 12” and 10” guns, of the last calibre at least 8.(1)

Note
1. Of the South Carolina or Michigan-class, consisting of the South Carolina and the Michigan built between 1906-1910 and with an armament of 4x2-30,5cm/12” /45 Mark 5 guns, 22-7,6cm/3” /50 guns, 2-4,7cm/1.46”/3pd guns and 2-53,3cm/21” submerged torpedo tubes.