XBradTC

URR here.  The United States found itself somewhat behind the Royal Navy at the start of the Dreadnought race, only laying down her first all big-gun battleships, the two ships of the South Carolina-class, three weeks after HMS Dreadnought herself was commissioned***.  Smaller and slower than HMS Dreadnought, the design of the South Carolinas, was however, in one way well ahead of its time.  

Built under the size restrictions mandated by a budget-conscious Congress, which limited US capital ships to 16,000 tons, the South Carolinas were the second-smallest Dreadnoughts ever constructed, only slightly heavier than Spain's two Españas (of 15,500 tons).   The 16,000-ton limit forced designers to compromise on propulsion.   The South Carolinas duplicated the machinery layout of their predecessors (and last US pre-Dreadnoughts), the Connecticut-class.  The proven triple-expansion engines, more fuel efficient than US turbines of the era,  produced a designed speed of 18.5 knots, about 1.5-2 knots slower than their British and German contemporaries.   Though South Carolina is said to have made 19 knots and Michigan 18.8 knots on builder's trials, their relative lack of speed limited their usefulness in a fleet action.  Despite that shortcoming, South Carolina (BB-26) and Michigan (BB-27) were surprisingly well-protected for their size and weight.  An armored belt up to 10" thickness, a conning tower of 12", and turret faces also of 12", met or exceeded contemporary armor schemes, despite the Congressional weight limitations imposed.  

What was it that made the South Carolinas so groundbreaking?  The answer is the arrangement of the main battery.  The ships carried eight 12-inch/45 caliber Mark 5 guns, arranged in two centerline superfiring turrets fore and aft, a layout that proved to be a generational leap in battleship design.  They were the first Dreadnoughts to mount their main batteries in this manner, and the tremendous advantage of this arrangement was readily apparent.   On a hull of the same size and displacement as the preceding Connecticut pre-Dreadnoughts, heavy gun power was doubled.  These ships could fire an 8-gun broadside to either beam without the need for additional main gun turrets.  The arrangement also gave these ships a more modern and balanced appearance than their contemporaries.  With the success of the arrangement on the South Carolinas, no US battleship would ever mount wing turrets in a main battery arrangement.

Most of the world's first-generation Dreadnoughts had main battery layouts that included wing turrets, for the purposes of maximizing broadside weight of fire. (Theoretically, wing turrets could fire across the beam, as well as broadside.   However, the immense blast damage, particularly when firing across the deck to the opposite beam, restricted any but broadside fire to absolute emergencies.)  In such wing turret arrangement, an additional two (or four) guns were required (in one or two additional turrets) to achieve the 8-gun broadside of the South Carolinas.  In addition, wing turrets meant that armor protection was required to be spread across a much larger area, and include more barbettes.  This further increaed weight and required a wider beam, with a concomitant penalty in speed.   

The careers of both South Carolina and Michigan were quite brief, spanning just eleven years in commission.  South Carolina was present at Vera Cruz in 1914, but that was the closest either ship came to seeing combat.  By the end of the First World War, the ships were thoroughly obsolete.   They were outclassed by much larger, faster, and more heavily armed super-Dreadnoughts, with increased compartmentalization, oil-fired boilers, and high-efficiency turbines.   Both ships served briefly after the war, but were demilitarized in accordance with the Washington Treat of 1922.  Michigan was to be scrapped, and South Carolina disarmed, briefly converted to a test vessel for torpedo bulge design.  By 1924, both battleships had been broken up.   However, the design arrangement for a centerline super-firing main battery, pioneered by the South Carolinas, would be a feature of all battleship (and indeed, almost all turret ship) designs to follow.  

***There is an oddity to note with the building of the South Carolinas.  For some reason, USS South Carolina, laid down several days after her sister ship Michigan, was given the lower hull number, BB-26, while her sister became BB-27.