Asklemmy

I gotta imagine that each planet in a sci fi setting would have its oen airforce, where as the compasion of space to a vast ocean makes sense for the organization tasked with patroling it.

I agree with what everyone else is saying, and...

Time of deployment on the vessel naval crews can be deployed from months maybe even years. Air crews are deployed for hours maybe a day. If the flight crew has a disagreement, they just have to hold their tongues long enough to land, and then they can deal with it on the land maybe even get reassigned etc etc

More analogies from naval service apply to spaceborn service where crews will be isolated for long periods of time.

Aviation and marine vehicles are both flying, just in different fluids.

Naval terminology is cooler.

"I'm the Captain of the USS Enterprise."

Vs

"I'm the Colonel of the Exploration/Reconnaissance/Fighter craft Enterprise."

In addition to what the others have said, in real life, international space law was based on maritime law. They even based directions on maritime law as the sailors used the stars to navigate, and that’s all you have in space to navigate with. So rockets and spacecraft call their directions the same as ships and sailing vessels, they have a port and starboard side, a bow and stern, up is zenith, down is nadir.

Fun fact the actual directions have some cool historical meanings. Nadir is the lowest point in elevation in the surrounding area, aka the bottom of the boat, and zenith is the area directly above you. So you could measure your latitude by measuring a star’s position relative to your zenith. Port was the side you docked on, because your steering oar was on your right. Starboard is a bastardization of the word stéorbord which is what the steering oar was called.

I'll agree with the other posters that being on a spaceship maps better to being on a ship than it does being in an airplane, but I would add to it one other maybe overlooked factor: Robert Heinlein served in the navy and clearly had a massive hard-on for it and included all sorts of pro-war and pro-military themes in his work, and that all came from the POV of the navy and included lots of specifically naval elements to what was presented, and he was a big enough presence in the field that it left a mark that lasts to the present day.

The purpose of Air Force is to monitor the skies, project power at a distance, and provide air superiority.

The purpose of Navy is to put a floating fortress off your shore and bombard your cities, carry around materiel, men, and aircraft, and patrol a vast volume of ocean.

So Navy structures fit the mission better, and this has been true since early SF.

They’re called “spaceships”

In the US at least, Air Force officer ranks match the Army and Marines. Sci fi tends to use those ranks for ground fighting teams.

Ship structure makes sense for a large ship. There is no similar aviation structure, the guy ultimately in charge is the aircraft is the pilot in command, generally the one flying the aircraft.

Some technical terms make more sense too. A hull is watertight, it translates well to a ship in space. A fuselage is describing the shape of the main body of an aircraft.

I guess the idea is that as in plying the oceans, you are looking at lengthy journeys in space requiring large vessels that can stock whatever supplies you need while protecting you from harsh elements with thick hulls. And they do talk about space fighters, which is more of an aviation term, but these are typically launched from the space equivalent of an aircraft carrier.

I think most generally it's because naval analogues are probably the closest when you're talking about large space-based fighting vessels. The air force doesn't operate aircraft carriers, battleships, or destroyers. The navy, however, does (or did in the case of battleships). Those large sea based vessels often class quite nicely into a lot of sci-fi media for large ships.

The small ships you see are often based off of a carrier equivalent. Even when they're terrestrially based, it makes a lot of sense to streamline your military structure to have just one "space force", rather than trying to break it up into two entities like the "space navy" and "space air force", each with their own standards and logistical supply networks.

I think it often has to do with the scale of the ship. Operations on a starship with crew numbering in the dozens to hundreds might be closer to operations on a naval vessel than aviation. We don't have aircraft with that scale of a crew or aircraft that operate away from base for such a long period of time.

The other thought is, uh, well that's what Star Trek did.