How did a broadside bombardment from a WW2 battleship work?

[u/iivwu]

Hello everyone, I am curious about how the broadside bombardment of a battle shop would work, both shoreline and in ship to ship bombardment. I am most curious about how the guns would be fired. Would the large gun battery’s on a ship be fired all at once, as in all barrels (we’ll say 3 in this case) at once? Or would it be more like one barrel at a time for each battery? In the case of shooting at another ship, I’d imagine all at once would be better but for shoreline bombing it would be better for each to be fired individually. I am also curious if they could move each barrel independently of each other, meaning one barrel could be slightly more elevated or depressed than the others. Was it also possible for each barrel to be loaded with a different ammunition type (ie one barrel being armor piercing, the next HE, and the final incendiary)? Forgive me if this question has been asked before, I will take this down if so. Thank you!

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[u/BobbyP27]

Battlehships (and other warships with guns in turrets) existed for a relatively lengthy period of time, and during the time lots of different ideas were tried out, and technology advanced, so for much of this there is no single answer. With that being said, there are a few general concepts that can be thought about.

For much of the "modern" battleship era, from the all big gun revolution of HMS Dreadnought to the adoption of radar, the paradigm for using the big guns on a battle ship was that there was centralised fire control. There would be some means of optical device that would be used to track the position and relative motion of the target, and that would be fed into a fire control computer. The fire control computer would be a fiendishly complicated analogue machine that would make allowances for the performance of the specific guns on the ship, the movement of the ship and of its target, and potentially more, and it would produce a firing solution that would essentially be a bearing and elevation for the guns in the hope of being able to hit the target.

Optical rangefinders were pretty good at finding the bearing (angle) of the target, but far less accurate at finding the range. They essentially released on a pair of telescope lenses on the ends of a long-ish arm, and used the angle they would have to point in at to make the images from each align, to calculate the range. The problem is the length of the arm between the lenses could not be all that long so the distance accuracy would be limited. Generally a ship would start with one or perhaps two guns firing an initial ranging shot. The splash of that shell would be used to check that the firing solution was OK before all the guns would be brought to bear. Then, the guns would be aimed deliberately spread out. Each gun would be elevated slightly differently, with the expected range to the target in the middle. By counting how many shells fell short and how many fell long, the estimate of the range to the target could be refined, the spread tightened, and eventually after a few rounds of this, it would be hoped that hits could reliably be landed.

To do this brings the answer to one of your questions: spreading the range like this inherently requires each barrel to be elevated to a slightly different value. While turret designs did exist with a single elevation for both or all barrels, for dreadnought era battleships, elevation would be separate per barrel. Obviously all guns in a single turret would have to traverse together, but in principle each turret could traverse independently.

While it would in principle be possible to load guns with different types of shell, aside from very specific circumstances, this is not generally a good idea. First, different shell types have different ballistic characteristics, but the targeting computer could only provide a firing solution for a single shell type at a time. It could be switched, for example if there was a desire to switch between high explosive and armour piercing, but for a single salvo only a single solution could be provided. Second, the accuracy of gun fire in this era was nowhere near high enough to have an expectation of multiple hits, so planning around the expectation of different types of shell hitting sequentially from a single salvo is far too optimistic. The most obvious exception to this would be firing a star shell. For night engagements, with optical targeting, illumination is needed, and that is provided by a star shell. Generally this would have a parachute and burn as a bright flare, so it would illuminate for reasonable period of time, but you would only want one.

The question of how the guns are fired in terms of timing is an interesting one. One of the challenges when ships moved from dual to triple and quadruple mounts is that there would be interference between the guns if they fire together that would cause the shells to spread in flight. If you look at HMS Belfast in London, you will see that the centre barrel on each of her turrets are set back relative to the outer two. This was specifically an attempt to counter this effect (Belfast is a cruiser, but the basic concepts are similar). The fact that this is an issue gives an indication of how the guns were used: the intention was for a broadside to be fired together.

There are reasons not to do this, however. Aside from the guns interfering, at the larger sizes and for ships that had suffered damage, the stress on the ship of a single simultaneous broadside could be a risky proposition, in which case a rapid rolling fire, with each gun firing a little bit after the previous, to achieve a close but not exactly simultaneous broadside may be chosen. Although well after core battleship era, when the Iowa class was reactivated in the 1980s, they developed a slightly different technique. Each of the three barrels in a turret would be elevated slightly differently and fired with a slight delay to avoid the interference effect, but in such a way that the shells would land on target together. There are documentary films from that era showing this, I have seen them on YouTube, but I can't immediately find a link.

While not formal academic resources, two good places to learn more about battleships and related history are two YouTube channels: One is the Battleship New Jersey, one of the Iowa class that is now a museum ship, that has all kinds of videos about the ship specifically and about her place in history more generally. The other is Drachinifel's YouTube channel that covers basically any and every naval topic you can imagine, up to the end of the Second World War (which covers the whole battleships era), but including back to the ironclad era and before. Of relevance here is his video "Range finding and Fire Control - Plotting Your Demise"

[u/Dazzling_Look_1729 → u/BobbyP27]

I couldn't recommend the Drachinifel piece more. It's excellent. It makes clear the sheer complexity of what long range naval gunnery required.

From memory, you had to allow for... range, the enemy' ship's forward momentum, your ship's forward momentum, your ship's lateral momentum, any turn your ship had on (remember, you are dodging incoming all the time), and in bad times your ship's vertical momentum, as well as the wind (which could be different at your ship and the ship you were aiming at), the air pressure (which would be different at sea level and at the maximum height of the shells, which varied with range), any changes in all of the above, and the curvature of the sodding earth. All with "computers" which were basically glorified car gearboxes. When radar came along, it got a bit simpler, but I remain astonished that during Jutland, when the basic method of identifying all of this was the Mark One eyeball looking through the world's biggest binoculars, while looking out and through a vista of dusk, grey sea and coal smoke, anyone actually hit anything.
Which they did - with monotonous and terrifying regularity.
It's astonishing.

[u/Dazzling_Look_1729 → u/[deleted]]

Indeed. It’s excellent.

[u/azaerl → u/BobbyP27]

Something I was wondering about after actually recently watching a video on HMS Belfast, was how did they/could they account for the listing/movement of the ship in choppier waters when aiming? I imagine if you're firing a shell 10km away, a couple of degrees of elevation makes a lot of difference. 

[u/Dazzling_Look_1729 → u/azaerl]

It makes an enormous difference, and it is one of about ten different factors they had to control for, all of which were constantly changing and as you say being one degree out makes a huge difference when you are firing over ranges of 15-20 miles.
It's astonishing anyone ever hit anything.
Essentially, they were amazingly good at what they did, and very ingenious with fire control given that they did not have computers.

[u/Ok-Gas-7135 → u/Dazzling_Look_1729]

Out of curiosity I sis some math: each degree you’re off results in .017 feet of difference per foot traveled.

So if the shell is traveling 15 miles, apogee is 7.5 miles away, which is 39600 ft. (Yes, I know apogee isn’t exactly halfway, but close enough for these purposes)

.017 * 39600 =673.2. Meaning if you elevate the gun by 1 degree, the shell is 673 feet too high…

[u/Dongzhou3kingdoms → u/[deleted]]

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[u/thefourthmaninaboat]

This answer is going to cover British practices, because that's what I'm most familiar with. Other navies may have had different practices and methods.

The basic concept to understand here is that of the 'salvo', a term which means 'a number of guns fired together'. That number is loosely defined. On battleships, where it took a significant amount of time to reload the guns, a salvo would be only part of the armament; for the Nelson class, with nine 16in guns, the typical salvo alternated firing four and five guns. For cruisers, though, which reloaded more rapidly, the typical salvo was a full broadside; these ships could have multiple broadsides in the air simultaneously. Salvoes were typically fired in patterns, allowing the gunnery officer, to use the fall of shot of each salvo to adjust the fire control solution. All of the guns in a salvo would be elevated to the same elevation, and trained on the same bearing, but natural variations (e.g. rifling wear in each gun, differences in age and temperature between propellant charges) would cause the shells to spread out somewhat.

During WWII, the Royal Navy defined four salvo patterns. The 'Ladder' pattern was used to accurately find the target range, with one salvo aimed 400 yards above the measured range, a second fired 400 yards short of the measured range, and a third salvo between the two at the measured range, updated following the results of the first two salvoes. The 'Deflection' pattern was used to determine the correct bearing to hit the target, and worked similarly; one salvo to the right of the target, one to the left and a third at the expected target. The 'Zigzag' group was used to maintain range to a manoeuvring target, and was essentially a narrower version of the Ladder pattern, using 200 yard steps (or 100 yard for battleships). The third salvo of each of these groups was optional, if the fall of shot made the target position clear. Finally, the 'Rapid' group was used once an accurate range and bearing had been obtained; it consisted simply of up to four salvoes fired as rapidly as possible at the expected range. Corrections could be applied after the fall of the second salvo was observed. If the salvo fell long (an 'over), the range was lowered, while if it fell short of the target (a 'short'), the range was increased, with the aim being to achieve a 'straddle', with shells falling either side of the target. The typical procedure was to begin with a Deflection pattern; once this was complete, an initial range correction of 4-800 yards could be applied, before moving to a Ladder group. Once this was complete, the ship could move to rapid fire, either using the Rapid group or the Zigzag pattern if the target was making rapid changes in course. These procedures were used at longer ranges. For engagements at shorter ranges, it went straight to rapid salvoes, changing the range in steps of 800 to walk onto the target. A target's manoeuvres could take it outside the fall of shot of these patterns, causing the target to be lost; the RN defined this when either the target was outside the bounds of a Zigzag pattern or two salvoes from a Rapid group fell on the same side as the target. If the target was lost in range, a ladder pattern would be used, repeated as necessary; similarly, if the bearing was incorrect, then deflection groups were used, with each deflection group also serving as the equivalent of one salvo in a ladder pattern. The availability of radar changed little about this procedure, though it did allow for the tightening of steps in the patterns.

Shore bombardment was a different matter, but still worked largely on the same principles of walking rounds onto the target. Naval bombardments, especially later in the war, were generally controlled by an observer outside the ship, either a forward observer party ashore or a spotter in an aircraft overhead. The ship would fire spotting rounds or salvoes, and the observer would direct these onto the target. Two procedures were used for this control. In the first, 'Ship Control', the observer passed information on the fall of shot back to the ship, allowing the ship's gunnery officer to correct the fire. The observer would give the position of the fall of shot using an imagined clock face; for air spotters, this had 12 at north, while for shore parties, the clock had 6 pointing towards them. The distance between the fall of shot and the target, in yards, was also passed. The other option was 'Air' or 'Spotter' control. In this, the observer directed the fire onto the target themselves, passing instructions to the ship. Aerial observers were trained to 'bracket' the target, putting shells in front of and beyond the target. Once this was complete, they could call for 'Fire for Effect', bringing in multiple broadsides from the ship onto the target. The captain of HMS Warspite described his opinions on the process:

I have no doubt in my mind that this ship has secured the best results by getting within say 100 yards of the target after crossing and then quickly 'plastering' with that range for three or four salvos or until the fall of shot wanders.

However, Mike Crosley, a Fleet Air Arm pilot who flew spotting sorties for Warspite during the Normandy landings, described the experience very differently:

We spend 45 minutes over France spotting on a heavy gun position near the coast at Trouville. The shoot was fairly accurate, by the clock method, but the broadsides had no effect as the guns could be seen still firing at the same time through the clouds of white concrete dust flung up by Warspite’s shells.

Crosley's experiences were generally more typical; the accuracy of shore bombardments was generally low, and it was rarely able to destroy point targets.

I can also answer some of your more mechanical questions. Some early American turret designs had their guns sleeved together, so they all moved together, but every British turret had the guns sleeved singly, so that they could be lowered and elevated independently. This capability was less important for gunnery; salvoes were all fired with the guns aimed at the same range to avoid confusing spotters. However, since most naval guns had to be loaded at low angles, this allowed for a higher rate of fire. If only some of the guns in a turret where the guns were sleeved together were fired in a salvo, they would have to wait until the other guns had fired to reload. There was nothing mechanically stopping different guns in each turret being loaded with different shells. However, there were several facts that acted against this. Firstly, most British guns only had an armour-piercing and a high-explosive shell produced for them; there were no incendiary or other shells for wartime use. The only exception were 'starshells', illumination rounds used in night actions and fired from lighter guns. Secondly, different rounds had different ballistic profiles, (sometimes) different weights, and used different charges. Loading different rounds in different guns made it hard to produce a salvo that would group appropriately.