Battleship secondary armament The secondary armament of a capital ship are smaller , faster - firing weapons that are typically effective at a shorter range than the main ( heavy ) weapons . The nature , disposition , size and purpose of secondary weapons changed dramatically as the threat changed . The Pre - Dreadnought Era . Pre - dreadnought s , from the period 1890 to 1905 , were typically fitted with 3 or 4 different calibres of weapon . The main guns were usually approximately 12 - inch caliber , secondary weapons usually 6 - inch but typically in the range 5 - inch to 7 . 5 - inch . Guns smaller than 4 . 7 - inch are usually considered " tertiary " . ( Many pre - dreadnoughts also carried 9 . 2 to 10 - inch " secondary " guns , but these are usually treated instead as a mixed - caliber main armament . ) Secondary guns were " quick firers " , and could fire 5 to 10 rounds per minute . It was this attribute , rather than their destructive power or accuracy , that provided the military value . Secondary guns were almost universally carried in " casemate s " , or a long armoured wall through which the battery of guns projected . Such weapons were designed to fire at both capital ship targets and smaller targets such as torpedo craft and destroyer s . Small targets were of course vulnerable to 6 - inch projectiles , and a high rate of fire was necessary to be able to hit a small and evasive target . In this era , secondary weapons were also expected to engaged capital ships . Heavily - armoured areas of battleships would not be vulnerable to 6 - inch fire , but there were large areas that could not be heavily protected . These lightly armoured and unarmoured areas would be " riddled " at the expected ranges of perhaps 3000 yards . This would knock out the enemy ' s secondary armament , punch holes in the lightly armoured bow and stern , perhaps knock down funnels and spotting tops , and destroy the bridge and command positions . In short , secondary guns were a very important factor in battleship combat . Dreadnought Era . Dreadnought s were characterized by an " all - big - gun " armament . Broadly , this era spans from 1906 , through the super - dreadnought era , to the end of World War I . During this period , there was some variation in the selection of secondary weapon . British practice , at first , was to mount very small guns ( 3 - inch and 4 - inch ) that were considered a tertiary battery . These guns were often mounted unarmoured in the open , or later , in a casemate battery . Later , the guns grew to 6 - inch size . In other navies , the 6 - inch size was commonly mounted throughout the era as a casemate battery . British doctrine at first held that the small guns were for anti - torpedo defense only . Other navies , with a larger secondary battery , held that they should also be used against capital ships . For instance , German doctrine , for fighting in the North Sea , held that poor visibility provided a good opportunity for the shorter ranges at which smaller guns would be effective . Britain later came around to this point of view , although the primary justification for mounting a 6 - inch battery ( in the " Iron Duke " class ) remained fighting against the increasingly large torpedo boats and destroyers . Naval historians covering this period disagree on the value of the secondary battery . Arguing for , it provided protection against surface torpedo craft without needing a flotilla of supporting craft that smoked up the range and burdened the admiral with additional command , control and signalling . Arguing against , it consumed considerable displacement ( 2000 tons or more ) , were holes in the side close to the waterline that increased the risk of capsizing , and could not be heavily armoured yet were connected to magazine s that threatened the destruction of the ship . There were also considerable difficulties in bringing secondary weapons into action with the main guns ; they too smoked up the range , splashed and obscured their target , and might required maneuvers to open secondary arcs that put the main guns at a disadvantage . Battle experience showed that capital ships were almost always accompanied by their flotillas , secondary batteries were ineffective against capital ships , and German battleship secondary batteries were very effective in the Jutland night action against British destroyers . World War II . With the emergence of the threat from air - delivered weapons , the nature of the secondary guns changed once more . Now they needed to be multi - purpose weapons , with a high - angle fire capability to engage aircraft , as well as the traditional use against destroyers . Although they were also used against capital ships , the extreme range of capital ship engagements ( through superior optics and target prediction and , later , radar ) , meant they were not expected to achieve much . High angle weapons could not be mounted in casemates . Thus , they migrated to small turrets mounted on the upper deck . In order to hit a fast - moving air target , a high rate of fire was required , thus secondary guns reverted slightly to the 5 - inch from 6 - inch size although 6 in guns were still used by several navies including France , Germany , Italy and Japan in new built battleships .