The upgrades require various techs to unlock.

I’m not sure. I’d have to ask. My understanding is that each type has its own set. By default, military buffs all nearby friendly ships for instance.

I believe each base has some core capabilities of defense. Example, I have a Economic Starbase that I can add the "Starbase Defense System" onto. Cost for that is one module. I can also use it to increase the production of my worlds, such as: Finance, Production, Research, etc.

I had to play with it for a bit as I assumed I would need a "Mining Starbase" to increase production output on my planets. Not the case.

The defensive upgrades for military bases are in the weapon/defense techs. Seems a little strange they cannot also use the same defense system as every other starbase, but they can eventually get stronger.

Note to devs: nothing ingame explains this: I was confused the first time I wanted to fortify a military base, too.

Please verify game files and start a new game.

Verifying game files 

Many issues can be resolved by verifying you have the most recent files. 

Epic:
 

If you have a savegame where this is reproducible it would help a lot if you uploaded it to a cloud service (DropBox, Google Drive, One Drive) and post a link here, so the developers can take a look at it.

Savegames are located in \Documents\My Games\GalCiv4\Saves

Thank you for the savegame.

Quoting Strange Jane9570,

reply 9

   

Thats nothing. I am trying to find the time today to replicate the issue were the military stations do not attack enemies (war declared by NPC) even if they are very close, attached, to them. 

I will report the bug, but was busy last two days and didn't play much to generate the 2 save files needed for the devs to investigate. 

any news? issue persist

Good stuff Derek, thx!