Main Guns Part 3

By 1907, the 12" gun had reached the limits of its development. Trying to improve range and penetration by throwing projectiles faster was clearly a losing game, so calibers began to creep up again. The British lead the way with a return to the 13.5" gun, to replace the 12"/50 used on some of their later first-generation dreadnoughts.

13.5" gun on HMS Ajax¹

Besides the accuracy issues already discussed, the 12"/50 suffered from an absurdly short barrel life. As a gun is fired, the hot gasses melt and erode the bore. This is more of a problem for high-velocity guns, and on the British 12"/50, the liner was worn out and had to be replaced every 130-160 rounds.² The 13.5"/45 that replaced it saw a significant reduction in muzzle velocity, from 2850 ft/s to 2580 ft/s, but an increase in barrel life to a full 450 rounds.³ Thanks to the improved ballistics of the heavier shell, the two projectiles were traveling at the same velocity by the time they reached 15,000 yards.

Turret and loading path similar to those on 13.5" guns of the Colossus class

It was soon realized that the British designers had been overconservative after the failure of the 12"/50, and that the 13.5" gun could be pushed further by using a heavier shell, at an acceptable cost in barrel life. The gun itself remained unchanged, although the hoists and other handling gear had to be modified to accommodate the longer shell. Below is a table comparing the 12"/50, the 13.5" with both the original 1,250 lb shell and the later 1,400 lb shell and the 15"/42 the British adopted to replace it.

The Germans took a very different approach, using 11" guns on their first dreadnought class, and then 12"/50 guns on all of their ships until the Bayern class of 1913. This gun surrendered only about 50 ft/sec to its British counterpart, and fired a 895 lb shell, but had a barrel life of approximately 200 rounds.

Cordite charge for 15" Mk I gun

The increased barrel life relative to the British 12"/50 was for two major reasons. First, the Germans were world leaders in metallurgy, while British industry was rather conservative. Second, the Germans used much cooler-burning powder, while the hot British cordite tended to cause rapid erosion. Despite this, it was still relatively short by British standards, although that might have been more acceptable to the German Navy, which was chronically cash-strapped, and thus much more economical with training than the RN. Ships were traditionally regunned when the barrel life was less than the per-gun ammunition capacity, to ensure that the gun was accurate at the end of a battle. Going from 130 to 200 rounds of accurate fire was thus a major improvement for ships which traditionally carried around 80 rounds per gun.

Animation of 15" Mk I turret

Of course, not everyone was willing to sit out the caliber race the British had started. The Americans and Japanese trumped the British with 14" weapons starting around 1910. Winston Churchill, then the First Lord of the Admiralty,⁴ was willing to continue, upgrading to 15" on the Queen Elizabeth class. No such gun existed, and he was gambling the fate of the 5 newest British battleships on it working. If the gun had proved a failure, the ships would have been armed with only 8 13.5" guns, a step down relative to their predecessors. Fortunately for him, and for Britain, it was a gamble that paid off handsomely, as the 15" Mk I was probably the best battleship gun of World War I. Accurate, reliable, and effective, it was also the armament of the last British battleship, HMS Vanguard.⁵

Monitor Lord Clive firing her 18" gun

WWI intervened, freezing British capital ship construction, although they'd already begun plans for an 18" gun, which ended up only being mounted on HMS Furious and some monitors.⁶ As it was, the next step came again from the Americans and Japanese, who both went to 16" for their ships starting around 1916. This limit was later enshrined by the Washington Naval Treaty, and the British built their only 16" battleships in the early 20s, the Nelson class.

Muzzle blast illustrated

As interesting as the guns themselves is how they were put on the ships. While it's easy to talk about fitting 8-12 guns aboard a ship, doing so in a way that allows the maximum number of guns to be brought to bear while avoiding structural problems and blast interference is surprisingly difficult. For structural reasons, turrets are most efficiently placed on the centerline, directly above the keel, but space there is limited. Heavy naval guns produce significant overpressure. A British 12" gun⁷ produced 30 psi of overpressure at 150' directly in front of the muzzle, and at about 70' directly beside the muzzle. 30 psi is enough to cause severe lung hemorrhage in people, and do severe damage to even reinforced concrete and seismic structures.⁸ This makes finding safe places for all of the other stuff that needs to go aboard a warship, everything from secondary guns to boats to bridgework, rather tricky.

Hexagonal (above) and Dreadnought turret arrangements

Many of the later pre-dreadnoughts had been fitted with wing turrets, cantilevered out to the sides of the ship. These were structurally inefficient and could only fire on one side, but were fairly common on early dreadnoughts, too. Dreadnought herself had 5 twin 12" turrets, one forward, two wing turrets, and two aft, both on the same level. In theory, this arrangement gave 8 guns on either broadside and 6 guns forward or aft. In practice, firing the wing guns close to the centerline was not popular due to blast damage. The original plan had been to use a 6-turret hexagonal arrangement, but the aft pair had been consolidated due to blast interference. The hexagon was later used by the Germans and Japanese on some of their battleships.

Superfiring turrets on USS Pennsylvania, with sighting port cutouts visible at the lower left and right corners of the wing gun ports

The American South Carolina used a different system to gain an 8-gun broadside, with only four turrets. Two turrets were forward, and two aft, with the second and third turrets elevated so that their guns trained over the outer turrets on each end. This arrangement, known as superfiring, was not adopted by the British due to concerns about blast effects on the lower turret if the upper turret was fired near the centerline. The Americans, who were less concerned with end-on fire, adopted the arrangement to meet restrictions on ship size. One major factor in this was the different placement of sighting ports. The British placed their sights in the roof of the turret, which made them vulnerable to blast effects. It wasn't until HMS Hood that the superfiring turrets were able to fire within 30° of the centerline. The Americans placed their sighting ports in the turret face, which was obviously much less vulnerable to blast.

HMS Colossus, showing staggered wing turrets and superfiring turrets aft

The biggest disadvantage of Dreadnought-style wing turrets was that one turret would always be out of action, at a considerable cost in weight. In an attempt to balance the advantages of wing turrets in end-on fire, the British produced the staggered wing turrets used in HMS Invincible and later on many battleships and battlecruisers worldwide. This was similar to the staggered turrets of some ironclads, where one wing turret was placed in front of the other, leaving gaps through which each turret could in theory fire across in the ship. In practice, of course, blast meant this was not a popular procedure, and on some ships was considered to be so dangerous that it was seen as more of an emergency capability in case the turret on the engaged side was disabled. Finally, around 1910, designers began to place all of the guns on the centerline.

HMS Agincourt, the ultimate turret farm

This wasn't a final solution to the problem of packing heavy guns onto ships, though. To go above 8 guns with twin turrets meant that space for fifth and sixth turrets had to be found on the centerline. This caused lots of problems on the resulting "turret farms". Often, steam pipes had to be routed around magazines, which resulted in uneven powder temperature and poor accuracy. It drove up weight and left little space for things like boats, which needed to be clear of blast. The most extreme of these ships, HMS Agincourt, had 7 twin turrets on the centerline.

US 14" 3-gun turret

The alternative to cramming on more turrets was to enlarge the turrets and fit more guns in each one. Besides saving considerable centerline space, a pair of triple turrets were considerably lighter than three twins. The major downside was that a triple turret is more complicated and slower-firing than a twin, as more is going on in a relatively smaller space, and there's no nice and symmetrical way to lay it out. A hit on a triple also disables more of a ship's firepower than a hit on a twin, but the tradeoffs were usually worth it. The Italians were the first to lay down ships with triple turrets, but they were soon joined by the Austro-Hungarians, Russians, and Americans.⁹ The British, Germans, and Japanese stuck with the twin through the end of WWI, while the French went straight to quadruple turrets for the Normandie class, cancelled because of the war. Triple turrets allowed sufficient firepower to be packed into the 4 turrets which could be easily fitted aboard a battleship.

USS Nevada showing 2-gun turret superfiring over triple turret

Before WWI, naval guns developed rapidly, reaching unprecedented heights of caliber, shell weight, and velocity. The practice of mounting them aboard ships also improved, from the inefficient wing turrets to the superfiring triples of the US Standard Type. Next time, we'll examine the development of guns after WWI, to the pinnacle of the type on the Iowa.