Planetary Defenses II: Turrets
What we started with
Base Sins' approach to defenses is that they are a delaying tactic to weaken enemy combat ships and provide basic defense against things like planet-bombing frigates. As such, the Gauss turrets and their analogues were well-armored but took a long time to reload and did mediocre damage. They were difficult to destroy, but only served one real purpose (which admittedly made a hell of a lot of sense in Sins' scheme of things).
What they did
Other mods have realized this way of doing things is a little constricting and that some planet defenses could be effective in a damage-dealing role. After all, they don't move, so you don't have much of an excuse to not avoid them. This is a start, but without effective mechanics in place to force more tactical defending and/or tweaks to Sins planet-bombing mechanics, players will simply place them at the edges of gravity well as bonus damage-dealers or in the same spots near a planet to cover them from attack.
What we did
This focus on an interdicting role for planetary defenses is a big deal in Dawn of Victory. As you saw with mines, walling a player into chokepoints is a great strategy. But eventually they'll make some sort of headway against your mines - especially later in the game, when strike craft are plentiful and cruisers can outrange them. Thus, it's necessary to reinforce your chokepoints with long-ranged turrets. While not as complex to disable as mines, turrets serve both the roles of damage-dealer and scary "i don't want to go there" structure. Mines are your passive defense, turrets your active defense. Mines are your sandbags, turrets are your ZIS-2s.
And like any artillery piece, turrets can be replaced by traditional mobile units. You could just as easily back your minefield up with a bunch of flak frigates and a few destroyers, or on the German side some speedy corvettes. But turrets are a quicker and cheaper investment and can be placed much more easily. They're also much more versatile: fielding a destroyer against a German cruiser is going to result in catastrophe, but a turret can do just as much damage to that cruiser as it can to a corvette or frigate because of its diverse damage types. More on this damage dealing aspect in a later journal this week.
Finally, each faction has a different sort of turret, diversifying defenses. The Soviet Union uses a all-purpose quick reloading, moderately armored Weapons Array with heavy flak and light torpedoes, while the German Reich uses a long-reloading and slightly less armored Railgun Platform with a long-ranged medium railgun.