Main armament power and caliber

Rather than try to fit more guns onto a ship, it was possible to increase the power of each gun. This could be done by increasing either the caliber of the weapon and hence the weight of shell, or by lengthening the barrel to increase muzzle velocity. Either of these offered the chance to increase range and armor penetration.[46]
The workings of a dreadnought’s main armament, based on the British 15-inch gun used on super-dreadnoughts

Both methods offered advantages and disadvantages, though in general greater muzzle velocity meant increased barrel wear. As guns fire, their barrels wear out, losing accuracy and eventually requiring replacement. At times, this became problematic; the U.S. Navy seriously considered stopping practice firing of heavy guns in 1910 because of the wear on the barrels.[47] The disadvantages of heavier guns were twofold: first, the required guns and turrets weighed much more; and second, heavier and slower shells needed to be fired at a higher angle for the same range, which affected the design of turrets. However, the big advantage of increasing caliber was that heavier shells are also affected less by air resistance, and so retain greater penetrating power at long range.[48]

Different navies approached the decision of caliber in different ways. The German navy, for instance, generally used a lighter caliber than the equivalent British ships, e.g. 12-inch (305 mm) caliber when the British standard was 13.5-inch (343 mm). However, because German metallurgy was superior, the German 12-inch gun was superior to the British 12-inch in terms of shell weight and muzzle velocity; and because the German guns were lighter than the British 13.5-inch, German ships could afford more armor.[48]

On the whole, however, the caliber of guns tended to increase. In the Royal Navy, the Orion class, launched 1910, used ten 13.5-inch guns, all on the centerline; the Queen Elizabeth class, launched 1913, used eight 15-inch (381 mm) guns. In all navies, the caliber of guns increased and the number of guns tended to decrease to compensate. The fewer guns needed meant distributing them became less of an issue, and centerline turrets became entirely the norm.[49]

A further step change was planned for battleships designed and laid down at the end of World War I. The Japanese Nagato class in 1917 carried 16-inch (406 mm) guns, which was quickly matched by the U.S. Navy’s Colorado class. Both the United Kingdom and Japan were planning battleships with 18-inch (457 mm) armament, in the British case the N3 class. However, the Washington Naval Treaty meant these plans with their mammoth guns never got off the drawing board.[50]
A 14-inch naval gun, as fitted to the King George V class treaty battleships

The Washington Naval Treaty limited battleship guns at 16-inch (410 mm) caliber.[51] Later treaties preserved this limit, though reductions of the limit to 11, 12, or 14 inches were proposed.[52] The only battleships to break the limit were the Japanese Yamato class, begun in 1937 (after the treaty expired), which carried 460 mm (18.1 in) main guns.[53] By the middle of World War II, the United Kingdom was making use of 15-inch guns kept as spares for the Queen Elizabeth class to arm the last British battleship, Vanguard (23).[54]

A number of World War II-era designs were drawn up proposing another move towards gigantic armament. The German H-43 and H-44 designs proposed 508-millimetre (20 in) guns, and there is evidence Hitler wanted calibers as high as 609-millimetre (24 in);[55] the Japanese ‘Super Yamato’ design also called for 508 mm guns.[56] None of these proposals went further than very preliminary design work.