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 from torpedo boats, to torpedo-carrying destroyers, to aircraft, to anti-ship missiles.

Pre-dreadnoughts, 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 "casemates", 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 destroyers.

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 engage 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. Secondary guns were a very important factor in battleship combat.

Dreadnoughts 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.

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