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Let's assume for the moment we're in an alternative history/steampunk sort of setting where oil/coal/explosives are exceedingly rare, but tech around electric generators, motors, and batteries are advanced.

As such, railguns are widely used rather than conventional explosive artillery.

Manufacturing techniques over the centuries have improved accuracy, durability, and weight. They started out as unwieldy, unreliable, immobile things best used as siege weapons. Now, it's World War Two era and they're still not terribly accurate but are durable enough to depend on. 15mm to 200mm rounds are about the tolerance of current manufacturing, the "barrels" are 2-3x the length of explosive gun barrels, and tend to be 5-10x the weight. Muzzle velocity is about 1500-2000 m/s. The power necessary to fire the gun takes more space though - tanks still look roughly like tanks with the space saved by smaller ammunition replaced with capacitors and added power generation.

To the question then: what would naval warfare look like in this WWII alternate history?

The weapons seem infeasible to mount to planes, and the smaller railguns are likely lethal to aircraft of the age simply by using ammunition that fragments as it flies. I imagine ships would need to be designed a little differently to get their less-ballistic weaponry to fire over the horizon (unless firing through water is feasible?), but a lot differently to protect against rounds that have significantly different damage models.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – Monty Wild
    Sep 15, 2021 at 13:42

9 Answers 9

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IMO, the result would be a weird mixture that would be most similar to WW1, if it worked at all.

Without explosives, there are no bombs, torpedoes, or mines, implying that

  • There are no dive bombers / torpedo bombers and therefore no aircraft carriers. Aircraft are relegated to scouting and communicating the positions of enemy fleets.
  • No explosive torpedoes also means no destroyers or submarines to worry about.

We are back to something like the Age of Sail, in which the side with the heaviest weight of fire wins.

The railguns fire at the velocity of 21st century tank cannon ("1500-2000 m/s" from the question) instead of the lower velocity of WW2 naval cannon (e.g. ~760-830 m/s for various WW2 naval guns) but this leaves us with a variety of issues. There are no HE naval shells in the scenario and the AP projectiles don't have any explosive filler in them either as the normally would.

  • Above a certain velocity, even a steel projectile will shatter on impact. From https://en.wikipedia.org/wiki/Armor-piercing,_capped,_ballistic_capped_shell , "However, it was found that steel shot tended to shatter on impact at velocities upward of about 823 m/s (2700 feet/second)" and, while the APCBC shell was created to ameliorate this, the stated velocity of the railgun is still too high for the cap to compensate for. Tanks get around this by firing APFSDS kinetic penetrators made of uranium or tungsten so you might get away with doing something similar. Another option is to fire a lighter projectile that reaches hypervelocity speeds where the composition of the projectile matters less because the impact converts the projectile to plasma, doing tremendous damage. The last option is the boring one: just fire a larger, ordinary WW2 APCBC projectile at the normal velocity for WW2 naval guns.
  • If you go the AP / kinetic penetrator route, you have the issue of overpenetration. The projectile simply goes right through the ship, punching a neat hole through anything it passes through, but otherwise not doing much damage unless it intersects with something important. A classic example of this is the Battle of Samar where much larger Japanese warships firing armor piercing shells at lightly armored US destroyers and light carriers had little effect because the AP shells simply passed through the ship entirely; the ships were destroyed only after the Japanese switched to HE shells. You may need to invent entirely new types of projectiles that are designed to optimize for damage against specific ship armor thicknesses.
  • Again, if you go the AP / kinetic penetrator route, another problematic aspect is that a ship is much, much bigger than a tank and the penetrator is very small, so you wind up in a situation where you're trying to poke an elephant to death with knitting needles. So the battle will be a prolonged slugfest until enough systems on the losing vessel are damaged to render it incapable of fighting. Though the range of the railgun is longer because of its greater power, battle range might actually be closer because of the relatively little damage each round does even if it hits; one would want to get close enough to reliably hit specific parts of the enemy ship to maximize the chance of crippling it without expending all one's ammunition or wearing out the rails on the railgun.
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    $\begingroup$ Yes, this. Also worth looking at tactics - given that impacts by solid shot at shallow angles are more likely to ricochet off than penetrate, tactics would emphasise trying to approach an enemy from their port or starboard while keeping them 5-10 degrees of your bow. Your shots will penetrate while theirs will glance off. For a fleet, it means "crossing the T" is exactly reversed. Armour concentration on a ship would also be similar to that on tanks - non-explosive rounds on ballistic trajectories would be low threat so thin top armour, heavy, angled front and side armour. $\endgroup$ Sep 7, 2021 at 23:57
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    $\begingroup$ As an aside, I came across this delightful 4 part series explaining the evolution of naval shot (solid projectiles) and shells starting from the Age of Sail to the end of the battleship era that begins here: navalgazing.net/Shells-Part-1 . Worth a read. $\endgroup$ Sep 8, 2021 at 3:45
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    $\begingroup$ How about a 'two-stage' railgun projectile where the first stage is itself a single-use railgun? You could fire a railgun torpedo or large tank shell which guides itself onto a target, then fires a penetrator from point-blank range. The first stage workings would need to be quite robust to survive launch and impact, but it would also mean you don't need to fire the first stage as fast, as the energy of the hit comes from the capacitor (or other source) inside the projectile. You could even have a gliding first-stage for extra range. $\endgroup$
    – Beejamin
    Sep 8, 2021 at 10:28
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    $\begingroup$ Overpenetration could be mitigated by using some sort of sabot round, that expands after leaving the gun to increase the size of the impact area. Old-style cannons used to do this with chain rounds - literally fire a length of heavy chain out of the cannon - these had less range but were brutally effective against soft targets (people) as well as masts, sails, and rigging, far better than traditional round cannonballs in fact. (Those were more preferred against the armored hull of the ship.) $\endgroup$ Sep 8, 2021 at 17:22
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    $\begingroup$ Why would aircraft not be build and used? They would remain excellent for scouting and dropping solid shells bunker-buster style to destroy infrastructure on the ships they attack, like the turrets and for much less risk than a full ship. The ships themselves have no flak or any type of timed/proximity fuses and the scattershot proposed by OP will likely not really be very effective, assuming a railgun can even do such a thing without damaging itself. I would say that while aircraft will be much diminished in power against ships, they would still be potent due to the lack of power ships have $\endgroup$
    – Demigan
    Sep 8, 2021 at 19:19
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Wooden monitors. With rams.

italian monitor ship

https://en.wikipedia.org/wiki/Italian_monitor_Fa%C3%A0_di_Bruno

The advent of railguns made any armor pointless. Even ironclads could not resist being punctured by a railgun round. The solution: keep wood as the building material (it is light, and cheap!) but move the entire hull below the waterline. Wood as a material offered another defense against railgun rounds - the round was liable to go right through the ship and out the other side. Ship hulls are made as lightweight as possible, and the neat holes produced by railgun rounds are easy to patch.

The result: monitors. Ironclad monitors existed in our timeline as a response to the move of explosive artillery type shells to naval use. Above is the Italian version which is pretty much a giant cannon and a spotting tower. The original USS Monitor of the Union navy rides even lower. Monitor type ships with railguns would be murderous against shore based targets. Targets on shore cannot hide underwater.

uss monitor https://en.wikipedia.org/wiki/USS_Monitor

But as regards ship-on-ship battles, water is better armor against railgun rounds than anything they could possibly put on the sides of the ship. Projectiles are not very effective against a target almost completely below the water. In a world without explosive shells or torpedoes, it would be very difficult for the monitors to use their formidable guns to damage each other.

Which leaves the way ships damaged each other before effective projectiles: the ram.

https://en.wikipedia.org/wiki/Naval_ram#Steam_rams

With the development of steam propulsion, the speed, power and maneuverability it allowed again enabled the use of the ship's hull, which could be clad in iron, as an offensive weapon. As early as 1840, the French admiral Nicolas Hippolyte Labrousse proposed building a ram steamship, and by 1860, Dupuy de Lôme had designed an ironclad with a ram.[12] The quick success[13] of CSS Virginia's ramming attack on USS Cumberland at the Battle of Hampton Roads in 1862 attracted much attention and caused many navies to re-think the ram...

The theory behind the revival of the weapon derived from the fact that, in the period around 1860, armour held superiority over the ship-mounted cannon. It was believed that an armoured warship could not be seriously damaged by the naval artillery in existence at the time, even at close range. To achieve a decisive result in a naval engagement, therefore, alternative methods of action were believed to be necessary. As it followed, from the same belief, that a ship armed with a ram could not be seriously damaged by the gunfire of its intended victim, the ram became, for a brief period, the main armament of many battleships...

The fast, lightweight wooden monitors could be cut in half if rammed by an opponent. And so naval duels between the railgun armed monitors become like the naval duels of millenia before, with ships jockeying to get position and ram their opponents in half.


It occurs to me that if projectiles barely work against other ships and ramming is tricky, the main form of naval action would be the boarding party. This occurred to the builders of the Monitor also.

https://en.wikipedia.org/wiki/USS_Monitor

Wise who was aboard and inspected Monitor after the battle responded in a letter of 30 April 1862: "With reference to the Monitor, the moment I jumped on board of her after the fight I saw that a steam tug with twenty men could have taken the upper part of her in as many seconds ... I hear that hot water pipes are arranged so as to scald the assailants when they may dare to set foot on her."[48] The chance to employ such a tactic never arose. There are conflicting accounts as to whether such an anti-personnel provision was installed.

@DWKraus reference to Verne's fictional battery-powered submarine Nautilus made me think of another method to repel boarders: electrification. Also good vs giant squid.

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    $\begingroup$ Ships that remain mostly submerged might also help counteract the massive heat generated by firing a rail weapon. $\endgroup$
    – JonSG
    Sep 7, 2021 at 22:21
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    $\begingroup$ There's a neat myth busters episode where they look at the ability of projectiles to penetrate water. Musket rounds went straightest and penetrated the deepest, while 50cal rounds disintegrated on impact with the water. That's why I went with gunboat submarines in my answer. The barrel pokes out of the water, and WHAM. Without explosives, I could see Nautilus-style subs as ramming vessels, especially if you went with wooden hulls... $\endgroup$
    – DWKraus
    Sep 7, 2021 at 23:31
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    $\begingroup$ Re: "the neat holes produced by railgun rounds" in wooden hulls, that's not quite right. The outside has only a neat hole but the backside erupts in a hail of rather large splinters; see, for example, youtube.com/watch?v=XfsuIaTU92Y . One would probably want the equivalent tank spall liners near crew stations to reduce injuries. $\endgroup$ Sep 8, 2021 at 2:11
  • $\begingroup$ Also, re: "Projectiles are not very effective against a target almost completely below the water", there is the example of Japan's (not all that effective) type 91 shell that was designed to enter the water near the target vessel and strike it below the waterline: warfarehistorynetwork.com/2016/07/01/… . There is also a Japanese Wikipedia entry (ja.wikipedia.org/wiki/…) on it that has more detail. $\endgroup$ Sep 8, 2021 at 5:17
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    $\begingroup$ The big disadvantage of wooden ships if hull structural strength. Would you be able to build wooden hulled ships big enough for the power systems for railguns? $\endgroup$ Sep 8, 2021 at 14:19
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Power is King:

You are creating technology to match your story. I suspect that the biggest difference will not be artillery, but in power generation. At a WWII tech level, the easiest way to move and generate power is to carry a combustible fuel with you. It is portable, semi-random access, and won't generally degrade on storage. What the form of that is, I don't know. But with how you describe it, these will be battery/capacitor-powered vehicles except at the largest level. Power plants will be rapidly deployed, and may even be extremely large vehicles (giant war machines! Yay!) The over-all feel of fighting might be WW1 if fought with 21st century machines, with the largest weapons only extending as far as a power cord. If you have Nikola Tesla-style wireless broadcast power stations, these will definitely be at the front line.

BATTERIES: But to have batteries or capacitors that can store enough energy to allow weapons platforms to function at all like the weapons of the era, you need radical differences in how materials are purified and produced. A tech tree is not a flexible willow, but a tough oak. You are likely to have advanced metallurgy, precision manufacturing (that applies across the board), and advanced communications and computing. In short, you will be closer to modern tech than WWII tech, minus fossil fuels.

FIREPOWER: Guns will be computer controlled, and extremely accurate. Radar would likely be sophisticated, so few surprises on the surface/in the air. Bombs and missiles will still be critical for aircraft to be useful in war.

ENGINEERING: Advanced materials will also allow fairly advanced engineering for aircraft. Abundant industrial electricity will allow abundant aluminum and lightweight construction. What you apparently don't have is sophisticated engineering outside of electronics. Planes and tanks will be underpowered and slow compared to modern ones, but perhaps appropriate for the WWII era. IF jets are just being developed like during WWII, they might be electric plasma jets. The same batteries/capacitors running your guns will run your engines. There is likely to be battery anxiety in commanders, and fixed artillery will remain extremely powerful due to abundant corded power.

SHIP DESIGN: Ships, on the other hand, are big. While you haven't explicitly said what they got their power from, it is likely ships will carry a power generation capacity with them. Designs are likely to be centered on ships with big guns for first-strike capacity. Bigger ships mean bigger guns, but also big, vulnerable targets. Engineering will likely concentrate on multiple redundancies and ability to function despite damage, rather than armor. The armor that does develop will possibly be reactive, composite-sandwiched from advanced materials or gel/fluid based, but may not look a lot like WWII armor.

TYPES OF SHIPS: So I'll guess few if any aircraft carriers (since without bombs airplanes will be badly underpowered). Battleship-type designs with lots of armor will be coastal bombardment craft. Minimum ship sizes will depend on power generation. The standard ship-of-the-line will likely be similar to a battlecruiser. They have enough armor to deal with inferior vessels, but big enough guns to deal with anything bigger.

SUBMARINES: With OP guns and comparatively weak armor, stealth and surprise will be crucial. I'll predict gunboat-submarines which surface (just barely, or only the barrel), fire weapons at point-blank range, and crash-dive to avoid return fire. High-velocity projectiles actually fare WORSE going through water. So torpedos and depth-charges may again be indispensable explosive applications to deal with the submarine menace. A big enough gun able to depress radically MIGHT be able to take the place of these, but the design would be to cause shockwaves, not impacts.

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  • $\begingroup$ @Alexander Fair point. Change made. $\endgroup$
    – DWKraus
    Sep 7, 2021 at 20:55
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    $\begingroup$ gunboat submarines would need UAVs or some other form of airborne asset to handle spotting. The spotting distance achievable from a surfaced submarine to line up a shot would be a significant restriction on railguns. Just look at some of the issues Surcouf faced. $\endgroup$ Sep 8, 2021 at 14:15
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Planes and electronic warfare

At the beginning of WW II, battleships were still seen as the best in naval warfare. At the end, it was apparent that aircraft carriers were key. Thanks to their long range airplanes, higher accuracy, adaptability and self support it was easily superior to battleships. This was in part to their explosives, which are rare in your world.

This isn't a reason to discount a repeat of these events in your world. War is about removing enemies their power. It is easy to think about destroying them, but there is a wide range that sometimes us preferred. Politics and propaganda can change the soldiers to fight others or lay down arms. But we're interested in disabling and capture. Many naval ships might not sink, but were still disabled and rendered inoperable for a long time. They need repairs or can be captured. Captured hardware can be used for your own goals. Captured soldiers as labour, political pressure or other worth you can get out if it. They can also be maimed and send back, causing a resource drain on the enemy.

Outright destroying might be difficult with batteries and railguns and no explosives. However, your warfare is electronic. So it makes sense to attack this weakness. EMP and the like are quite powerful and can take out several electronics of the enemy, requiring new cables, transistors and chips before the machines can operate again. Disabling ships or tanks can give you the opportunity to fire with small railguns on the planes, or move in closer with the bjgger ones on ships and vehicles. Just that alone can make forces surrunder or be made close to a none-threat.

There's more though. Explosives are simply a way to transfer a ton of power in a short time, hoping to break something. Bullets as well, though more directional. Yet 'slow' energy release can be very effective. That is where the, presumably better, battery technology comes in. In real life they aren't afraid of phones exploding in airplanes, but of the batteries starting to burn. Electronic fire is a big problem. It is hard to extinguish, can quickly reach crazy temperatures, sets other fires and besides the normal bad smoke of fire there's heavy metals and bad chemicals that can add literal layers of death and destruction. Make a 'bomb' out of it, chuck it on a ship and hope it'll destroy in excessive heat for long periods of time.

The better weapons against planes might seem detrimental, but the cost vs gains is still excessive. A naval ship just costs way more than a few planes. Besides, the lower speeds of planes meant that hits generally were less catastrophic than on the fighter jets nowadays. There's plenty evidence of planes staying aloft while looking like a pinata, as long as some key area's weren't hit. That means they might get close enough for ordinance to reach their target, despite getting hit.

Railguns and battleships would again go to a more supporting role, while aircraft carriers with a multitude of roles, armaments and abilities can rain down death and disabling devices on the enemy.

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    $\begingroup$ While I disagree with how much you can get out of aircraft, I do see a great potential in the electrical or EMP equivalent of a landmine. They could even be corded and reusable! $\endgroup$
    – DWKraus
    Sep 7, 2021 at 19:07
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    $\begingroup$ @DWKraus you might be right. With fictional scenarios it is easy to see ways airplanes can be underpowered. I still think it has a decent chance myself. Corded EMP landmines or, if possible in the water, seamines would be very powerful in such a world. Disabling can in many cases be stronger than outright destruction. At the very least it takes something out of operation for likely long times. $\endgroup$
    – Trioxidane
    Sep 7, 2021 at 19:15
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    $\begingroup$ I hadn't been thinking of EMP when I wrote my answer. One downside to purely EMP attacks: if the systems are robust, EMP doesn't really affect batteries. Battery-powered tanks/planes resistant (unless you fry the other components). This COULD be a plus for aircraft. But motors might get cooked, so might not matter. Redundant systems in Faraday cages? Guessing these folks would be really good at hardening their electronics. $\endgroup$
    – DWKraus
    Sep 7, 2021 at 20:31
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What will you see in terms of naval warfare? Almost no change whatsoever.

Rail guns are very impressive, but in the end, they only do two things: provide longer range within a smaller space. Why do I say this?

  • Because you can throw a rail gun slug a lot further (well... assuming modern tech...) than you can a chemically-motivated slug.

  • And the space needed to power a rail gun plus the ammunition for the rail gun is a lot smaller than the space required for the same kinetic impact in terms of shells and powder. (Granted, this assumes that you're using nuclear power. You're using something a whole lot more impressive than fuel oil to use rail guns, otherwise you won't have nearly as many rail guns in play and they won't have a significant impact on combat).

But you still have line of sight tracking. In other words, unless you allow for satellite tracking (invented in 1959, the naval Transit tracking system for tracking submarines) or some form of AWACS (invented in 1977), you're stuck with the fact that you can only "see" as far as your ship-based radar will allow you. And that limit is the horizon.

And the horizon is the key to success

A rail gun could certainly throw something beyond the horizon, but without the ability to aim it, you're just taking pot shots. That's the value of an airplane and the reason aircraft carriers became (and remained) the dominant naval craft. An airplane can fly beyond the horizon.

In short, other than sinking the Bismarck sooner or perhaps not evolving battleships at all... nothing will change.

Rail guns would make the faster cruisers and destroyers more valuable than the heavily laden battleships. This might be the only significant change — there would be little to no need for battleships as everything they did could be accomplished (and probably improved upon) by rail gun carrying and much cheaper to build cruisers and destroyers. Here's why:

Thanks to airplanes, by the end of WWII all battleships (world wide) had been retired or relegated to supporting roles. These roles were not insignificant.

  • Battleships were still quite deadly at night when planes couldn't fly.

  • Battleships were still used for coastal bombardment. Planes, especially bombers, could do a whale of a lot of damage and could reach further inland than battleships. But if what you want is a good old fashioned Baptist bible thumping, nothing could deliver the message more thoroughly than a battleship.

IMO, the faster rail-gun-enabled cruisers and destroyers would outmatch battleships for night maneuvers. I'm not entirely sold that they'd settle the argument as completely when it comes to a coastal bombardment (after all, dropping a 1+ ton shell bespeaks authority), but the ability to turn a little bit of that sand into glass on impact... yowzah.

But, all things being equal, would battleships really not exist?

And here's where I conclude that nothing would change. At the beginning of WWII the world (notably the U.S.) were building battleships — honking big boats carrying honking big guns. So, really, what would change? You'd still have navies building honking big ships with honking big rail guns and that would continue right up until the first patrol of planes from an aircraft carrier somewhere over the horizon sank the first slow-moving and very-expensive battleship. (Never underestimate the effects of economics.)

So, really, I don't believe a thing would change with one really minor exception: engagements would be a bit further apart.


NOTE: An early parenthetic deserves a highlight: rail guns need a whomping amount of power. I might be wrong, but I believe all ships today that use rail guns have nuclear reactors. You simply can't produce the power needed to use a rail gun with anything less unless there's just one rail gun on the ship and the vast majority of the ship's volume is given over to battery storage, meaning you have a substantial recharge time. This would mean rail guns are relatively rare and are good for basically only one or two shots ("Aaaaah! Rail gun! Shoot the rail gun! Shoot! Shoot! Shoot!"). Are you handwaving this? Nothing would really change either way, but striking a ship full of batteries that have partially charged would have a dramatic result ("No boom today. Boom tomorrow. There's always a boom tomorrow."). You'd find that supporting ships will not want to be anywhere near them.

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    $\begingroup$ They'd be stupidly tall to see as far as possible over the horizon, which is stupid, and that's why the program is defunct, +1. $\endgroup$
    – Mazura
    Sep 8, 2021 at 8:48
  • $\begingroup$ Are planes sinking a Battleship with purely kinetic weaponry? I'm not sold on battleship relevance but the current dismissal seems unconvincingly presumptive. $\endgroup$ Sep 8, 2021 at 15:33
  • $\begingroup$ @SomethingSImple By "purely kinetic weaponry" I assume you mean bullets and bombs. A rail gun is a kinetic weapon. Planes sank battleships (Pearl Harbor), aircraft carriers (Midway...) and destroyers using bombs and torpedoes. Planes changed the nature of naval warfare. If you think I've been presumptive, the OP would be benefited by posting an answer explaining your position. $\endgroup$ Sep 8, 2021 at 21:16
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    $\begingroup$ @JoinJBHonCodidact how are the planes sinking battleships in a world where they(the planes) don't have access to explosives(ie bombs and torpedoes)? your answer doesn't address this at all. $\endgroup$ Sep 8, 2021 at 21:36
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    $\begingroup$ @SomethingSImple I ignored it because it's an imbalance that's impossible. No explosives means no ships, no planes, no anything (and explosives aren't non-existent, they're "exceedingly rare"). The OP will have a hard time explaining high carbon steel without the fundamental chemistry of explosives. $\endgroup$ Sep 9, 2021 at 3:36
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In addition to what @JoinJBHonCodidact said, here's some more reasons railguns with the stats described in the OP don't make much difference.

First, assuming the highest-end muzzle velocity, a railgun will have a maximum range of about 57 miles. An Iowa-class Battleship had a maximum range of 24 miles, with a muzzle velocity of 820m/s. 2000/820 = 2.4, so your railgun can shoot 2.4 times further than an Iowa-class battleship. This is not a huge advantage today. Missiles can go thousands of miles.

Second, armor penetration is not improved by additional speed beyond a certain level. At a certain point, adding speed stops penetrating deeper and just makes a wider hole. So it will still make sense for battleships to be heavily-armored, and likely in similar armor configurations.

Third, remember what I said about faster projectiles making a bigger hole? Well there will be more material blown out of the impact hole, or knocked off the inside of the armor plate in the case of a railgun shell, since it's faster, and this shrapnel should make up for a lack of explosives.

Fourth, traditional battleships could shoot over the horizon in real life; they used spotter aircraft to help direct their fire. No reason you can't do the same thing with balloons or zeppelins or something.

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WW2 was seeing the beginning of nuclear powered naval craft. This is a strong candidate to explain the power generation aspect.

Now as to the projectile physics, the US Army does have prototype railguns. Check this out. https://www.defensenews.com/naval/2021/07/01/us-navy-ditches-futuristic-railgun-eyes-hypersonic-missiles

The project was killed, but mostly because missiles are just better. Your world being limited on such technology, railguns should be a strong contender. They do have relative slow firing rates though (mostly because of the capacitor charging time). You could magic science this away on account of "advanced electromagnetic tech", and add in a gatling system (if you don't need the full power of let's say 6 caps, you can shoot with only 2, then the next 2, then the last 2, and by the time you're done, your first 2 caps can be recharged).

Now, a BIG problem of railguns is that they don't work underwater. The core physics principle is having to "hot" rods, and a conductive projectile that going through them, shorts out the open circuit. The projectile is propelled by the resulting magnetic field, as the capacitors are quickly discharged from one rod to the other, through the projectile. Put the whole thing in water, and you won't be able to charge the thing at all, all the energy goes into the water. Or let's say you disconnect the rails during charging, you would still lose a significant amount of energy due to shorting. Perhaps consider Gauss cannons (coil guns)? These can be made water resistant, and could be viable for submarines.

As to airplanes, up to you, whether the weight is acceptable or not. Consider that the bulk weight of a railgun is power related. So decide if the needed batteries/capacitors are too much or not. You can give planes limited firing capability, as they would have no power generation of their own, but instead carry batteries enabling them a limited number of shots.

Keep in mind, you can't have anything more than rudimentary propeller planes, if you move into jet engine territory, you will also have missiles. And missiles have been proven as the superior tech.

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Say room temperature superconductors were discovered in the 1870's, around the same time that Maxwell was summarizing electrodynamics. Then I could see a world like this naturally evolving. One where you can efficiently generate power from the wind, and transport it as far as you want with no losses. Coil guns are way more efficient, and so are electric motors. Naval warfare would have 2 components. First you would have carrier-sized coil gun artillery platforms, which turn the power from the ocean's tides into death and destruction 400 Km away. Second, you would have fleets of ultra-fast submarines trying to sink their opponents artillery platforms, while avoiding the counter-sub subs.

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The railguns:

"Regular" ship canons would load a shell and several bags of propellant. For different ranges they would put in different amounts of propellant. Your railguns likely use various capacitor banks, by selecting how many banks are emptied per shot they can adjust the range and fire rate. After all if you only empty half your capacitors on a barrel per shot you can fire the next one almost immediately. This can be useful when you want to use plunging fire or reduce the overpenetration on a target.

The ammo:

With explosives out of the picture you need to look into the materials used in the shells. A "hollow point" shell designed to break up or mushroom inside the ship for example or using other materials than explosives. Pressurising a shell with a dangerous chemical to incapacitate the crew or damage components like the wiring inside the ship could be helpful. Regardless all ship to ship combat would take longer than normal.

Since the shells aren't blunt objects the impact depth will still increase with higher velocity, besides that secondary effects of high velocity will still be present. Such as shrapnel, buckling and spalling.

Ship armor:

With high shell velocities and not a lot of advanced material research it makes little sense to try and truly stop the aerodynamic shells from impacting. However you still need armor against shells designed against overpenetration.

The outer line of the ship will be a whipple shield*. This shield is designed against small-arms, as any gunboat with a railgun machinegun could rip through the entire ship from stem to stern and damage the vitals like batteries without it. Since larger shells of the enemy will be designed to break up and scatter as much shrapnel through the ship it is likely most ships will heavily compartimentalize everything.

Torpedo's:

Early torpedo's were electric. Without explosive filler torpedo's will act differently: they'll contain a small railgun inside and deploy a "parachute" to push off against the water to resist recoil. They will deploy the parachute and fire the canon upon impact with the enemy ship. Since aerodynamics aren't necessary at that range the shell fired can be various shapes to maximise damage as it is launched into the hull.

Ship to ship combat:

Like in the real world, at some point there is no reason to bring a bigger gun anymore and it is more useful to bring many smaller calibers to increase fire rate and hit chance. Railguns will hit this mark sooner, so 200mm rounds will likely not exist. Having a bigger ship would become a liability rather than an advantage since even a small ship can severely damage you. It is likely most big ships will simply have a lot of dead space inside where shells can pass through safely in order to hide vital components and have an easier time fighting against a small and compact ship where hits are more likely to disable something.

Aircraft:

Since sinking a ship is harder without explosives all fights will take longer. This means that aircraft still have a role to play. They can scout out enemy ships and drop bombs to try and damage the ship infrastructure or try to kill the crew. In return the ships also have a mixed bag in AA fire. On one hand they will be missing fuses for flak projectiles, especially the proximity fuse was vital for American AA defenses. On the other hand the higher velocity of the bullets and shells means you don't need to lead that far ahead to get a hit, but you have to hit them more often since you aren't showering them with shrapnel (a shotgun-like railgun would not really work).

Like in the real world the cost/effectiveness per plane is simply higher. That makes aircraft efficient. Although the smaller ship sizes would make the differences less pronounced.

*https://en.m.wikipedia.org/wiki/Whipple_shield

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