Received a lot of questions on Military Bases this past week so here is an explanation on how they work.
First you need to build a Military Base ship. The planet's current Tec Level becomes the Tec Level of the Military base ship. Build code for the Military Base Ship is 253. Next you need to land the Military Base ship on the intended planet. The action code for landing a Military Base Ship on a planet is 127.
Now how the Military Base works once installed on the planet.
The military forces on the planet fight at the Tec Level of the Military Base, meaning Forts, Fighters, Marines, and Heavy Marines. Since fighters can also be launched against other planets and fleets they fight at the Tec Level of the Military Base on offensive operations as well.
While a Military Base on a planet does not increase the overall Tec Level of the planet, meaning any ships built on the planet are the Tec Level of the Planet, not the Military Base, it does allow you to build ABM's on the planet if the planet Tec Level is not at least 18. It also allows you to build higher Tec Level torpedoes on the planet or retool the torpedoes to a higher class.
The only way to upgrade a Military Base on a planet is to replace it with a new Military Base Ship.
Military Bases cannot be attacked by Missile Ships or Guerrillas but will be destroyed if the planet is successfully invaded.
Military Base Ships can be retooled to a new Tec Level same as any other ship.
Military Bases can detect alien ships in System Space if they are scanning the system same as a high Tec Level planet.
Military Bases also act like high tec planets when probed, meaning they can capture the probe before it transmits data back to the owner, give you the name of the probes owner, and even send back false data to the probes owner, thus masking the planet from it's true stats. High tec planets do the same thing as an FYI.