Secondary armament
The first dreadnoughts tended to have a very light secondary armament intended to protect them from torpedo boats. Dreadnought herself carried 12-pounder guns; each of her twenty-two 12-pounders could fire at least 15 rounds a minute at any torpedo boat making an attack.[57] The South Carolinas and other early American dreadnoughts were similarly equipped.[58] At this stage, torpedo boats were expected to attack separately from any fleet actions. Therefore, there was no need to armor the secondary gun armament, or to protect the crews from the blast effects of the main guns. In this context, the light guns tended to be mounted in unarmored positions high on the ship to minimize weight and maximize field of fire.[59]
12-pounder anti-torpedo boat guns mounted on the roof of a turret on Dreadnought (1906)
Within a few years, the principal threat was from the destroyer—larger, more heavily armed, and harder to destroy than the torpedo boat. Since the risk from destroyers was very serious, it was considered that one shell from a battleship’s secondary armament should sink (rather than merely damage) any attacking destroyer. Destroyers, in contrast to torpedo boats, were expected to attack as part of a general fleet engagement, so it was necessary for the secondary armament to be protected against shell splinters from heavy guns, and the blast of the main armament. This philosophy of secondary armament was adopted by the German navy from the start; Nassau, for instance, carried twelve 150-mm (5.9 in) and sixteen 88-mm (3.45 in) guns, and subsequent German dreadnought classes followed her lead.[41] These heavier guns tended to be mounted in armored barbettes or casemates on the main deck. The Royal Navy increased its secondary armament from 12-pounder to first 4-inch (100 mm) and then 6-inch (150 mm) guns, which were standard at the start of World War I;[60] the U.S. standardized on 5-inch (130 mm) caliber for the War but planned 6-inch guns for the ships designed just afterwards.[61]
The secondary battery also served several other roles. It was hoped that a medium-caliber shell might be able to score a hit on an enemy dreadnought’s sensitive fire control systems. Also, it was felt that the secondary armament could play an important role in driving off enemy cruisers from attacking a crippled battleship.[62]
The secondary armament of dreadnoughts was, on the whole, unsatisfactory. A hit from a light gun could not be relied on to stop a destroyer. Heavier guns could not be relied on to hit a destroyer, as experience at the Battle of Jutland showed. The casemate mountings of heavier guns also proved problematic; being low in the hull, they proved liable to flooding, and on several classes some were removed and plated over. The only sure way to protect a dreadnought from destroyer or torpedo boat attack was to escort it with its own destroyer squadron. After World War I the secondary armament tended to be mounted in turrets on the upper deck and around the superstructure. This allowed a wide field of fire and good protection without the negative points of casemates. Increasingly through the 1920s and 1930s the secondary guns were seen as a major part of the anti-aircraft battery, with high-angle, dual-purpose guns increasingly adopted.[63]
