I just want to know if there is any purpose to having a water navy in a sci fi universe where you don’t really worry about countries on your own planet attacking you, since you’re the only one there.

I just realized that perhaps I should talk about technology, as this could help. The technology is not as advanced as seen in other sci fi series. So, for weapons, all military in the small patch of stars with all these civilizations use the standard array of military planes. Fighters, bombers, attack, cargo, all that. They also have helicopters or something similar, like for example this neighboring alien civilization which our Union of stars tends to have conflict with use ornithopters. Most planes have spaceflight capabilities, and helis can be sent down with the help of cargo aircraft. Some planets use airships, which are kept on the planet. There’s always an army, which can be sent down in large spacecraft. The army uses standard guns, although there are railgun and coilgun artillery and large laser weapons used to cut aircraft apart while they are flying. They use tanks with normal gunpowder fired shells, as well as shell firing artillery. There’s a specialized marine force as well which use high tech multi environment suits. There’s a space force for planetary Defence. Space combat would work like in the expanse, with basically the same weapons. Gatling guns, missiles, railguns, as well as coilguns which aren’t seen in the expanse I don’t think. As for what technology I would think that these naval ships would have. Well, ciws Gatling guns, small cannons, ship to ship missiles, torpedos, aircraft, if it is an aircraft carrier, as well as railguns, coilguns, and lasers. I also imagine there would be stealth submarines.

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    $\begingroup$ @PcMan Water navy might be cheaper than sky navy. $\endgroup$
    – Daron
    Oct 30, 2021 at 18:18
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    $\begingroup$ @PcMan We currently have the ability to fly huge, fast vessels around. We still have ships. Ships float of their own accord. They do not fly of their own accord. Economics rule. $\endgroup$
    – Mary
    Oct 30, 2021 at 18:50
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    $\begingroup$ @Mary What huge ships do we fly around that are anywhere even remotely as big as marine ships? Let alone huge and fast ships. $\endgroup$
    – DKNguyen
    Oct 30, 2021 at 19:12
  • $\begingroup$ @PcMan Do you mean long tons or short tons? $\endgroup$
    – Daron
    Oct 30, 2021 at 20:29
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    $\begingroup$ If your planet abandons defending the oceans, that sounds like a great place for an invading planet to start invading from $\endgroup$
    – BruceWayne
    Oct 31, 2021 at 1:26

17 Answers 17


Depends on the exact details of your planets, but some uses for a Navy/Coast Guard:

  • deal with pirates
  • deal with smugglers (probably of contraband, not for tariff evasion)
  • other law enforcement on the high seas
  • rescue operations at sea
  • $\begingroup$ A police navy is still a navy! $\endgroup$
    – Joe Bloggs
    Nov 1, 2021 at 8:29
  • $\begingroup$ It's not (as far as I know) ever stated what it actually does, but Star Trek has a Federation Naval Patrol. I have always wondered what that was for, but I imagine something like this. Though why a spacestation or ship with transporters and scanners can't just beam everyone into custody or out of danger as needed 99% of the time I have no idea. $\endgroup$
    – diwhyyyyy
    Nov 1, 2021 at 14:34
  • $\begingroup$ @Inductiveload I believe in ST: ENT, after a major attack by a space weapon that took out a large swath of Florida, the Naval Patrol was involved in rescue operations. The amount of affected area there was probably a bit too much to just beam out all the survivors. $\endgroup$ Nov 1, 2021 at 15:28
  • $\begingroup$ @DarrelHoffman Not wanting to get tooooo far into comic-book-guy territory, but it seems like an event that overwhelms transporter capacity (i.e. every transporter on the planet since the range is ~40,000km,, plus every warp-capable ship within a few hours of the planet) is also likely to overwhelm a navy, unless it's extremely over-provisioned the other 99.9% of the time, and/or has extremely fast ships that can load, move, unload and return faster than mass parallel transport. Admittedly in ST:ENT transporters were new, but they were old hat by the timer Tom Paris wanted to sign up. $\endgroup$
    – diwhyyyyy
    Nov 1, 2021 at 17:43
  • $\begingroup$ @Inductiveload Yeah, come to think of it, the newness of transporters probably factored into that (the show pretty much only used them for cargo except under duress), and there also weren't that many warp-capable ships yet either. So the Navy (and probably Army, Air Force, Marines, Coast Guard, or whatever planetary military forces existed) were probably a lot more involved than they would've been circa ST:VOY. $\endgroup$ Nov 1, 2021 at 19:40


There might (I stress might) be a role for submarines as part of a planetary defense/security system. You could hide key facilities deep underwater and use subs for crew transfers and re-supply etc.

If your government is dictatorial having a squadron of nuclear missile armed subs available on any planet with large oceans would also be a deterrent against rebellion.

You could just as easily put these in orbit either as satellites or on a station etc but given time the rebels can always locate these since orbits are by default predicable. Also people would presumably travel up to and down from orbit on a regular basis and its possible (although perhaps unlikely) that rebels could take control of orbital weapons and disable them. They can't do that with subs if they have a human crews.

Also most of the subs would be at sea at any one time. This means even though the rebels would know they existed and could perhaps attack/infiltrate their home ports (secure island bases would make this harder) 7 out of 10 subs or more would always be out of reach. Albeit no system is fool proof unless some tech exists that lets you track them is real time subs would be really hard to locate, not before they launched anyway.

Beyond that? As per the other answer all such planets, regardless of waht type of government they have might find a coast guard/air sea rescue service to be of value.

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    $\begingroup$ toughsf.blogspot.com/2017/10/anti-orbit-laser-submarines.html $\endgroup$ Oct 30, 2021 at 12:12
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    $\begingroup$ Yes, I considered things like that. Problem is those types of weapons can be deployed anywhere on the surface of a planet and arguably are better off deployed in orbit if you have the capability to do so. This is especially the case in scenarios (like this one) where you control those orbits and any threat has to approach from space. At the very least this means you don't have to waste power on punching a beam through the atmosphere on the way way to the target or on boosting a missile from the surface up into orbit. $\endgroup$
    – Mon
    Oct 30, 2021 at 23:19
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    $\begingroup$ Subs to carry surface-to-orbit weapons? An invader from space could never be sure that they're all gone and that it is safe to send in unarmored freighters. $\endgroup$
    – o.m.
    Oct 31, 2021 at 5:12
  • $\begingroup$ True, But if they control the high orbits and the solar system in general it doesn't really matter. The battle is lost when th4 orbits are lost. They can simply issue an ultimatum 'surrender or die'. And if they do that the it doesn't matter how many subs you have. The enemy can choose to put just one ship in orbit (as a show of force) and if you attack it they bombard the planet. And there's nothing an entire fleet of subs can do to stop them! $\endgroup$
    – Mon
    Oct 31, 2021 at 11:00
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    $\begingroup$ Nuclear missile submarines are important for second strike capabilities when your enemies have the ability to simultaneous disable all your fixed silos, but that level of force is going to require state-level action. Nuclear missile subs would have no real purpose against a rebellion that lacks a nuclear arsenal or overwhelming ground forces. If you're really worried about rebels neutralizing your entire array of nuclear missile silos, it's hardly a setting where one government controls the planet. $\endgroup$ Nov 1, 2021 at 13:41

Aircraft/Spaceship carriers

An external surprise attack would obviously start from fixed defence facilities on land. Among them there would be also the airports to prevent a counter attack. Submersible Aircraft/Spaceship carriers would remain underwater constantly moving to avoid detection by spy drones end emerge when needed.

Too much water

Ground support on a planet almost completely covered by seas.

Keep the local population under control

A sea base fore that could hit anywhere on the planet from an unpredictable direction would discourage rebellions.

Militarise the population

Carry out police and civilian duties using a military force just to justify military spending and population control.


Welcome aboard, @Epicgamermoment!

It sounds like you're not necessarily trying to rule the possibility of wet navies out?

It could be that you're interested in having a water navy on one (or some) of the planets within in your unified government. This is a pretty legit creative theme: water navies make for some very compelling storytelling and worldbuilding.

The answers so far are all looking to find reasons why or why not, and they have come up with some pretty good ones. But notice that those answers are all dependent on features of your created world. There's nothing about the existence of an interstellar government, as such, that either prevents or requires waterborne military capability on the individual worlds.

In general, I think you have several key worldbuilding features that might be considered:

  • The nature of interstellar travel. You didn't say exactly how the interstellar civilization travels between star systems. The most common idea is to have starships; a less common fictional means of getting around is the "stargate" idea, in which long-distance matter transmission, at FTL speeds, is reliable and capable enough to knit your interstellar government together. Note that these two suggested technologies have very different implications: A gate does not automatically imply the arrival of large armed vessels in orbit, capable of providing overwhelming military presence. (Your gate might be stationary on the surface of a planet; or it might be quite small in aperture, suitable only for passage of individuals, or small cargo carriers.) And even if you are using starships, there are plenty of possible tweaks you can do with the ship technology. Your starships might be quite small, and/or expensive to operate. Your starships might be, for engineering reasons, too fragile to be combatants themselves. Etc.
  • What causes a need for military forces in the first place? This is vaguely alluded to in your question: "you don’t really worry about countries on your own planet attacking you". Still, this is a big deal. Who does fight in your multistellar state? Why? What do they fight about? You specifically seem to doubt that there will be multiple "countries" on a given planet -- but why? How much political authority does the central power have? It could be reasonably weak, and still hold together. And then there's the question of whether a nation-state is the only entity capable of organized violence. @Ash raises this explicitly, and well, in their answer, but @Mary, @Mon, and @FluidCode all address the issue, at least implicitly. After all, would the Fremen in Dune be considered a "country"? :-)
  • What's the nature of military equipment? The key advantages of water travel are that you don't have to build roads or rails, and that it's cheap to move very heavy things (as @Mary says in a comment above, "Economics rules"). So maybe water transport is an excellent option on at least some of the planets. How do they project power in your civilization? Big heavy missiles? Attack aircraft squadrons? Massive ray-gun emplacements, so big that they must be emplaced on solid land or on large seagoing platforms? Or... (going back to Dune again) knives and swords?

...Not trying to smother you here! More like, hoping to inspire you. Worldbuilding is a whole lot of fun. Speculative exploration of various aspects of the world you're creating can lead you down some very creative paths.

So, the general Worldbuilding answer to your question is, If you want water navies you can have them. It's your world to build.

  • $\begingroup$ My idea for interstellar travel was where you could tunnel into the 7 dimensions theorized in string theory, where distance inside of there is shorter than in 4d space, meaning that a short distance in what I’m gonna call stringspace, means shorter distance in 4d space. $\endgroup$ Nov 2, 2021 at 21:31
  • $\begingroup$ As for the need for a military, there’s another humanoid alien civilization similar to our own in terms of technology. So earth, Mars, Ceres, the Jovian system, and other stations and moons and planets with a government have formed a Union. Think of it kinda like the EU. This Union has a Cold War with these aliens, which sometimes heats up and can become super deadly interstellar wars. $\endgroup$ Nov 2, 2021 at 21:35
  • $\begingroup$ And finally the military equipment. The different militaries have a space force with warships that work kinda like the expanse in terms of space combat. They are equipped with CWIS, missiles, railguns, and coilguns. They also have an Air Force, in which planes can go into space to be transported to other planets, as well as well as an army and marines. For ground equipment, they use normal guns and wheeled/treaded vehicles. Marines have special super expensive armor as well, but use normal guns. $\endgroup$ Nov 2, 2021 at 21:42

The Empire is historically recent.

Your planet is controlled by one government. It was not always so. 200 years ago your planet was a fractious group of quarrelling countries. Then the offworlders from the Empire showed up and summarily added the planet to the Empire.

Now there is putatively one government. There are still several different cultures and languages. Persons are still suspicious of the people that their great-granddaddies fought against. People still practice the old ways, just in case.

The Imperials are not dopes. It works for the Empire that constituent nations of a world remain suspicious of each other, relying on the threat of imperial intervention to keep peace. Also it is a source of pride to the families that they are still hereditary Sea Knights, now swearing alliegence to the Emperor instead of the old king.

Plus you never know when the Empire will quit sending governors and representatives and it will be back to the old ways. Best to stay ready.


Non-state actors, read pirates and rebels, may be an issue at sea that warrants military action, necessitating a navy even on generally united worlds. In a multi-stellar civisation an argument can be made for the oceans and seabeds of inhabited worlds being heavily populated and exploited and it is possible that semi-independent entities (corporations and socially/economically/ideologically isolates) existing wholly on or under water may maintain naval style forces for self defense from other, similar, entities.


Layered defense.

Most sci-fi pretents that an enemy can deal with the space-based assets like an orbital defense platform without the planet doing anything, then once the space-based assets are gone the planet is at the mercy of the ships above "because gravity well".

However many sci-fi has ludicrous power generation. A single kilometer long ship has a reactor of immense power, besides that escaping the gravity well is almost a non-issue. See for example Halo's Pelicans being able to reach space and orbital speeds without any rocket, or Star Trek and Star Wars making hovering a multi-ton ship in atmosphere a neglegible experience. Such technology also makes kinetic bombardment from space a non-issue to defend against. But that reactor is microscopic compared to electrical plants you can (and we do) build on a planet. Any logical planetary attack in such case would need to deal with planetary defenses and simultaneously with the space based assets. That means landing ground forces as well to try and shut down those planetary defenses.

Which is where a navy comes in. On a planet like earth and with the technology available, building military assets on the seafloor is a smart move. Even if kinetic bombardment is possible, the volume of water above the installations works as a shield and means you can focus on pressure-related protections.

A navy can then be used to provide surface and subsurface protection with the ability to move. Such ships can each carry their own power generation, and without the need for space-based living and FTL and other protections they can still provide a lot of firepower. This would be easier than on a land army, and its also harder for assaulting forces to land large multi-ton ships compared to a few mechanized infantry and tank groups.


Imagine a large energy facility designed to float at 1km depth beneath the sea surface, with engines to slowly move it about. This facility has multiple tethers of kilometers length that provide power to those floating oil drill facilities. Only instead of oil drilling it houses a giant canon capable of firing beyond orbital targets. The facility and platforms can move in relation to each other and across any sea deep enough. This does:

  • any bombardment on the sea facilities will fail unless you are very close, since you cannot predict their positions based on previous scans.
  • any long-range bombardment on land-based military and civilian targets will be picked up and defused due to powerful planet-based and space-based listening stations. Lasers and plasma projectiles can be diffused or torn apart by magnetics and kinetic projectiles can get a tiny nudge from an explosion or even ablation and end up missing the planet by millions of kilometers. Assuming the setting does not allow shield generators to be places just off their path and deflect/absorb the projectiles in a succession of shieldwalls they have to pass, or that antigrav tech can interact long enough to stop them or similar solutions.
  • any short-ranged bombardments means your system has already worked: your enemy is now close enough to be engaged by both space-based and planetary assets, and the atmosphere might make it hard to still pinpoint your sea assets while you most certainly have enough scanning equipment on the surface and in space to find them.
  • $\begingroup$ Of course, if you're throwing around the sort of multi-gigaton energies that Star Wars and Halo warships use, I suspect that once your wet navy ships opened fire and the enemy returned fire, they'd start rapidly boiling the oceans around them... $\endgroup$
    – nick012000
    Oct 31, 2021 at 11:50
  • $\begingroup$ @nick01200 but that is the beauty of it. You first have to boil that ocean before you get to the actual "destroy" stuff! Also the problem with "boil the ocean" is that just because the water has boiled, it hasnt disappeared. Additionally the advantage of moving facilities to avoid easy targeting until you are on top of the target is unmistakable. And with the amount of starships in these settings it is already a powerhouse to have 5 anti-orbital canons the size of a drilling platform, and you can have multiple. $\endgroup$
    – Demigan
    Oct 31, 2021 at 11:55
  • $\begingroup$ Well, once the oceans have boiled away, your mobile cannons aren't going to be very mobile anymore unless you include some sort of back-up antigravity - which you might want to do anyway, since boiling water provides less buoyancy than non-boiling water. $\endgroup$
    – nick012000
    Oct 31, 2021 at 11:57
  • $\begingroup$ @Nick012000 compared to a stationary land-based equivalent you already have all the advantages out of it long before the seas have boiled away. Even if they remain stationary afterwards. The idea of adding some backup antigrav or thrusters for temporary use is a solid addition. $\endgroup$
    – Demigan
    Oct 31, 2021 at 15:06

While my native country (singapore) has one of the more 'powerful' navies in the region - to a significant extent, its not really used in combat with other navies.

There's a lot of roles a navy can play - even with a 'dedicated' coast guard

  • search and rescue: Larger navy ships can act as a mobile base for air based and underwater searches. For example the search for the MH370 involved mostly military vessels at first

  • Natural disaster relief: While not quite as impressive as the american supercarriers (which are a small city on the sea), our LSTs tend to land supplies more than tanks. The british also have dedicated logistics ships that might be useful in this role

  • Anti Piracy operations: Just because there's a central, strong government dosen't necessarily mean there's no criminal element. They might have repurposed or smuggled in armaments. There's no need to chase them into space, and orbital bombardment is generally considered excessive so you might need local protection and discouragement via excessive planetside firepower.

  • Kaiju! While the "intelligent"/Dominant species of the planet might have government, the local megafauna has a tendancy to sometimes be a bit crochety. While ideally these creatures are discouraged, when you have a 200 ton lizard monster occasionally deciding to walk into a city, and scratch its back on the local landmarks, it might be useful to have a navy capable of using something a little more persuasive than the planet's largest rolled up newspaper. Likewise, there may be problem kaiju that might unfortunately need putting down . Fortunately this is not something our local navy needs to deal with at the moment but who knows!


Sea Navies are there to help monitor for rebel spaceship emergency landings, but also for non-rebel spaceships requiring a Splashdown landing

One thing about other countries on the planet that would likely cause an issue is landmass - if there's enough landspace for interplanetary travel via spaceships, which country houses which landing pads would be a contentious issue - since that could be farmland, or residential building lands, or mountains, or...

Thing is, other planets could be contacting via spaceships, and the landing pads sort of likely need to exist for communication, and supplies, or the transport of people between planets.

Which means you'll have a lot of details around immigration and exports/imports in the country, and you'll want to cut down on rebel smuggling attempts and such. If an unauthorized spaceship attempts entry, they could choose not to even land at your landing ports, and just land in any ocean, or on a deserted island, and stay hidden. Not great for a world government. But since you'll have to check the oceans and seas anyways, that seems like a great place to put your official landing ports for official, authorized travel.

So, what you'll want to do is have your sea navy in charge of air traffic control essentially for interplanetary travel - when you attempt to land, the following happens:

1.) You contact the local sea navy by planetary comms from outside atmosphere asking for an entry point, with maybe some guidance on which continent or city you want to depart at;

2.) The sea navy gives you coordinates to land at sea near the departure point, and send their landing pad out to that coordinate.

3.) You then enter the atmosphere, aiming for a targeted landing at that location.

4.) You hopefully* land on the landing pad at sea.

5.) You're transported by a ferry accompanied by the local navy ships and end up at your destination.

6.) Your ship is docked such that, for takeoff, you can take a landing pad out to see and launch off of that once you're ready to leave.

*This keeps the country from having to worry about mishaps in landing mistakes - instead of setting fire to a landing pad on land, and having to worry about their forests as much, if you do cause a fire explosion with a mistaken landing, they can just dunk the landing pad or your ship into the water to reduce the effects. Ideally, this doesn't happen, but if it does, that can be contained safely.

Anyone attempting to land without these steps is probably a rebel, so you encounter them with the navy if they land in the sea - which is likely their easiest target anyways, because there's likely to be a lot more water that is safe to land at than land with cities, or farmland, or notorious parks.


A really simple reason would be that space travel is extremely expensive. So a new colony’s tech and ability to get around is relatively primitive. On a new colony, more primitive travel by sea becomes absolutely vital. Vital enough to protect.

Centuries ago the populace arrived after a long sub light journey with limited and basic tech needed to seed a colony. Space travel is extremely expensive and limited to long journeys of ark ships that take decades or longer to complete.

On earth we take land travel for granted with our improved roads and rail systems. We also don’t consider how muc infrastructure we need for air travel. In particular air travel is extremely fuel intensive.

On a more primitive planet, or like Earth not to long ago, water based travel would dominate early. While it requires expertise, it’s expertise that can be taught to colonists readily using extrapolated star charts. Colonists can use the skill to navigate almost immediately upon arrival.

As centuries of development go by, some land and air capabilities develop. Yet the importance of the sea forms the backbone of the colony’s economy and culture.

but we’re all “unified” why do we need a militarized navy?

Even if organized under a single government, no group of humans is ever truly “unified”. Just look at our modern history.

Your planetary politics are far from simple. The ruling class must enforce its will from time to time. An unpopular law might make some happy but others extremely unhappy. The arrival of new offworld automation technology or immigrants might threaten a regional industry, leading to strikes.

If naval travel forms the backbone of the economy, you will absolutely protect the sea lanes with deadly force.

If sea travel is the most accessible form, it will be the cornerstone of how you project power around the planet.

  • $\begingroup$ Humans have access to ftl travel. Basically there’s another dimension which you can travel into. A good analogy is the nether from Minecraft. A certain distance traveled in the overworld=a shorter distance in the nether. So if you travel an overall distance in normal space, that distance will be far shorter in this extra dimension. $\endgroup$ Nov 4, 2021 at 0:25

Another path to take is that the navy could be a legacy force left over from an earlier time when it was necessary.

It made sense then but makes less sense now. Which could be acknowledged\lamp shaded in the story.

For example, they navy might still exist for political reasons because somebody powerful or influential has a stake in it, as a place to retire or transfer troublesome people to to keep them out of the way, or because they obliged to maintain it for treaty reasons or due to a contractual obligation to a private military contractor.

The navy could also be used as an outlet to train cadets before they are send into the much more dangerous environment of space.

Maybe it's just a playground for the sons of wealthy or influential famiiles.

  • $\begingroup$ For a while there was an Austrian Navy while Austria was landlocked; it was left over from the Austro-Hungarian empire, $\endgroup$
    – pjc50
    Nov 1, 2021 at 11:18


Serving on an ocean-ship is very similar to serving on a space-ship. You are isolated with a large number of people in confined space for a long time, you are surrounded by a deadly environment and you need to perform your technical duties to keep the ship running.

However, the ocean is a lot less dangerous than space. Sure, it's not harmless either. People can fall over-board and drown, and a serious accident can sink a ship. But all of that is nothing compared to the dangers of the vacuum of space. Decompression is deadly, and a ship which gets lost might have no hope to ever be found.

So serving on a ship for a couple month is used as a training exercise before personnel are considered ready to serve on board of a space vessel.


You've got o broaden your horizons. The navy does not exist for the sole purpose of naval combat.

According to the navy's anthem:

Where can you find pleasure
Search the world for treasure
Learn science technology
Where can you begin
To make your dreams all come true
On the land or on the sea?

Where can you learn to fly
Play in sports and skin dive
Study oceanography
Sign up for the big band
Or sit in the grandstand
When your team and others meet?

Why, in the navy of course!

Many people in the real world join the armed forces and they never get to go to war. They always get some nice education and perks, on top of learning proper discipline.



The oceans of one planet in the empire harbor dangerous megafauna. They are big (far bigger than anything on Earth) seem surprisingly intelligent at times and they do not like humans. Which makes them a serious threat to seafaring transport vessels (which are still more economical than flight), underwater mining operations and coastal regions.

So that planet needs a well-armed navy to fight those creatures.


Museum ships

On Earth today, one country alone has preserved 3 cruisers, 8 battleships, 5 aircraft carriers, and countless other auxiliary vessels, including a nuclear submarine. And we barely have 1 space station, and robotics is in its infancy.

Right now they sit in dockside, with contracts prohibiting their operation, and their material condition is too poor to permit sea operation.

Maintenance being the rub

Maintenance is hard in the early 21st century. Outer hull sheeting on a ship is basically ablative, will rust through and needs to be replaced from time to time. The museums, using charity money, must out-bid commercial and naval interests for a scarce commodity: dry-dock time.

Because it's hard to weld underwater. For humans.

But as a society moves toward interstallar travel, materials science at this level just gets ridiculous. Now hull repair is done by robots who are happy to work underwater, so the ships intentionally let to "silt up" are re-floated so the robots can work. Volunteer contributions only need to buy steel, electricity and robot repair... or simply deploy "replicators.

The upshot is, every museum ship is in "like new" material condition.

There would be no reason not to

To a very limited extent, some naval museum ships do operate. But navies do not like it when a museum ship is re-sold and winds up in the hands of an adversary navy, as did happen with a Soviet aircraft carrier. So navies have strict rules on making nothing operational except lights and ventilation.

In a single world government, these rules become irrelevant relics of bygone times.

So there would be no restriction on operation except the volunteer bandwidth to do so. An interstellar society is likely to have a great deal of affluence and leisure time. So that won't be a problem.

And indeed, there will be reasons for doing so. Natural disasters still happen (especially if the society screwed up their environment on the way to the stars). An aircraft carrier makes fantastic refugee accommodations for about 10,000 people. And so aside from museum and re-enactment duties, the museum ships are kept busy doing social good.


A modern navy could still be hyper effective for (last-ditch, emergency, trap yourself inside a kessler-syndrome-doom for 10 years minimum*) planetary defense. Think massive buoyant space flak cannons. Fired down into the ocean initially(or pulled down by motors on each corner) as the entire mechanism gains speed returning to the surface, an air-sensitive trigger at 1/3 barrel length (closer to top) triggers the actual firing of the cannon so the forces can compound and launch up to 2 tons of small piece copper wire, tiny ball bearings, etc directly into low orbit, preventing any object from landing unscathed.

*or maybe they have effective clean up that only takes a month in a post-conflict environment?


I love this question. People have it all the time. I think the naval (as in Naval naval) aspects of sci-fi universes is tragically overlooked. To ask this question, we ask 3 others; why does a scifi universe have infantry? or air units? or a space military?

To quickly bypass these questions you did not ask, the infantry exists to control and exert control, the air units can serve many purposes not limited to inexpensively transporting resources and personnell across the planet and providing air support against encroaching spacecraft, and the space military is mainly to intercept these different elements before they can ever reach your precious worlds. Also, orbital bombardment.

So, how does a sea navy fit into this? I find it kind of simple; look at todays battleships and acknowledge the purpose they serve. A modern battleship is essentially a mobile army base and defensive platform. It can shoot down aircraft, intercept ICBM's, transport great numbers of troops and supplies, and even launch aircraft of its own among many other things. In an FTL sci-fi world, I could only see these abilities being enhanced and the scope of possibility for your navies expanded.

Some major limitations of the usefulness of modern navies is that they are slow, incredibly expensive, require very large crews, and require a lot of maintenance. This could be very easily solved with FTL-level technologies. Think ships powered by fusion reactors and spaceship engines for propulsion, with AI mainframes commanding the ship and only a small crew of engineers and battalions of infantry waiting below deck to be deployed at the site of the enemy invasion line. Missile submarines, powered by advanced technologies, barraging large spacecraft with missiles from the depths of the sea. Submarine destroyers becoming a necessity for defense of cities anywhere near a coast in case the enemy drops one into their waters, and aircraft carriers maintaining their unmatched ability to deploy large numbers of small and low-range aircraft to swarm the invading enemy at its heart. To summarize: The ability to counter nearly everything, translated into especially slow and large targets such as spacecraft and maintaining dominance of the skies against smaller faster craft and atmosphere-restricted aircrafts.

Naturally, the limits of this concept are only the bounds of your imagination. But, I hope these ideas help ^^; Good luck!!


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