Here's a sort of ridiculous example for Halo: Gun-spacestations and gun-spaceships

Well, in Halo lore, the UNSC makes ample use of coilguns. These are projectile weapons that use a series of magnetic coils to accelerate metal projectiles at high speeds. They exist in real life, but only experimentally, but as of the 2550's when most of the halo games take place, the UNSC has a ton of them.

These range from the versions used in turret emplacements and on the backs of certain warthogs, to larger mass drivers used to launch waste into the suns of colonies or as anti ship weapons such the onager, which is the size of a blue whale to the one present on Concord, which is so big an entire large vehicle based multiplayer map is built around it and it extends way into the skybox, to the point where you can't even capture all of it in one screenshot and need to stich a 360 degree panorama to see the whole thing at once.

But we aren't talking about that pussy shit. Oh no. You know how in real life the A-10 thunderbolt aircraft was built just so the Gau-8 minigun had something to be strapped to? well, the UNSC makes much, much larger coilguns, called MAC guns which are so absurdly, obscenely big that their spaceships are literally built around them, with the MAC gun running near the entire length of all their main ships, to orbital space stations that SOLELY exist just to provide the MAC guns a platform to be build on and to maintain them.

You know the first mission of Halo 2? The entire mission just took place one one of these giant cannons (in fact you can see the main cannon firing at one point in the mission, as seen here, though since the player isn't looking at the floor you lose some of the sense of scale, this video might help in that regard), or super MACs, which fire projectiles so big and so fast (4% the speed of light) that somebody did the math: one merely being fired in the atmosphere would create an explosion the size of central europe just from