While there are obvious fluctuations most of the civilizations are on roughly the same level of military technology, each always striving to make the big breakthrough that would shift the stalemate, but nobody has managed yet.

Vessels will tend to run on fusion reactors, using missiles for long range attack. Warheads vary by purpose, but the old fashioned thermonuclear bomb is always a popular choice. Closer range involves mass drivers, lasers and particle beams in batteries that have so far proved more effective bang per buck than single massive cannons. Economic viability aside the last Zebulon applied war studies craft with a giant spinal mounted rail cannon was best described by the Imperial Fleet Marshal as ”that is going to ruin somebodies day, somewhere, somewhen.” to which his adjutant replied, ”Sir Isaac Newton remains the deadliest son of a bitch in space milord?”

Defence focuses on point defence lasers and mass drivers to intercept missiles and fields to deflect beams and projectiles. The principal remains the same as personal shields what changes is the power required to maintain the field and harden it against multiple simultaneous impacts, some of which have potential energy equivalent to nuclear weapons. To try to offset this large capital ships have secondary directional shield generator that can be used almost like a buckler on a person to take the brunt of fire from their largest foes. When all those things have failed you there is the traditional armour plating and an internal structure designed to be structurally sound, self consistent and modular even after large chunks have been blown off.

Of course there is the huge elephant in the room: The ardanium glide surface. Any interstellar warship must have a significant surface coated in ardanium. This creates a number of issues: Y your cost is increased massively, The ardanium must be a complete surface, that means one flank of your ship is just an ardanium plate, that gives your enemy a flank where you have fewer defences to shoot, Damage to that shell strands your ship until it can make repairs, giving your enemy two excellent reasons to shoot at that section.

The basic strategy is to have point defence cannons that deploy and retract and another directional shield purely for defending the ardanium face, the expense and complexity still leaves the ardanium underbelly far weaker combat-wise than the other facings, and capital ship maneuvering tactics is centred around to try to get your topside facing their underbelly. Other solutions have involved a retractable shell - a giant, complex moving part, or on one of the Distributed Process warships the entire section detached once jump had completed - effectively the warship arrived on a giant ardanium surfboard.

The problem with all of those is that they serve to compound the single most basic problem of interstellar war: the cost. Even taking out the tactical weaknesses and assuming that an interstellar warship is equal to a system defence ship, the simple fact is that for every ardanium plated interstellar ship you build, your enemies can build several system defence ships and still have change for an orbital battle station and weapons platform.

Experiments have been done into carrier vessels by most of the biological species, only to find them disappointing - while they seem attractive at first, the carrier with its expensive ardanium stays back and sends in the smaller cheaper fighters to the battle, economy of scale is an issue. It is simply easier to scale up engines, fusion reactors and weapons. When you scale them down you increase cost and lose power, to the extent that they are mostly ineffective against capital ship defence fields so nobody has bothered with them for serious war.

System defences make use of tachyon detection grids to detect incoming vessels. The ruptures in dark matter caused by a gradient endpoint produce numerous tachyon flashes that can be detected and triangulated. Worse for attackers, the size, frequency and timing of these is directly proportional to both the speed of the incoming vessels and their mass. Meaning that the bigger you are the louder you are, and the longer before you arrive that they get told you’re coming.

A continual worry among the biologicals is that the Distributed Process, who operate on different rules due to their inorganic nature, may be able to utilize strategies, tactics, weapons and defences that the organic races cannot, and that their current tactical doctrines have no counter against.

This makes all out aggressive shooting war a prohibitive action, that deep down all the civilisations are reasonably keen to avoid right now, at least until they can do something to get a decisive upper hand. Everybody's wargames conclude that if a full on war starts between any 2 players it will result in economic ruin for all parties and the only way to win is not to play.

Humanity has fought the most wars in recent memory: 3 to all counts:

The first was the Jihad against the Zebulon to recover the Qubba, which can best be described as an abject failure, and worse the Imperial military being tied up with the attack and fallout allowed for the second.

War number 2 was the rebellion, which is probably the largest fronted shooting war in humanities history as the Imperials moved to reclaim their rebellious colonies while trying to shut down the Jihad with the Zebulon as fast as possible as a colossal mistake. In the end economics ruled and the imperial commanders concluded that retaking all the colonies that they had spent the last decades arming and equipping with defences would at best be a pyrrhic victory, so they drew a line on the star map with what they could hold and peace broke out.

War number 3 was the second revolution, a last ditch attempt to stop the Federation falling into corporate fascism. The revolutionaries came to the horrible realisation that while some colonies had joined their cause, there were too few of them to mount a further attack. Worse there were sufficiently few of them compared to the remaining Federation that even though it would cost the Feds far more to retake their systems by force than it would cost them to defend, the Feds would be able to pay it. So those who were die hards took everything they could and fled, forming the Cooperative, and the Federation re-annexed the remaining colonies back with a minimal organised resistance, the Federations reacquisition of its colonies is probably the only war in recent memory where the aggressor definitively “won”.

When the revolutionaries liberated CORE, the AI that went on to found the Distributed Process, its act was not to join with them as they hoped, but immediately depart. While nobody in the biological races has ever asked why, it is not hard to imagine that the advanced AI, upon crunching the numbers of the current conflict, and comparing those to the massive wastes in proceeding conflicts, decided that it was a stupid idea, especially when it had available voyagers of internal and external exploration in its new sentience and the rest of of the galaxy.

The issues of conquest are perhaps best described by this transcript of a simulated wargame run by Imperial Fleet command to launch a sneak attack on the Federation colony of Beta Cetti 3, where the commander decided to go for a straightforward attack plan.

Fleet Admiral Wilbur: To be sure I understand the rules of the game Colonel Lowig played the Imperial forces, with the objective of the conquest of the planet and major orbital structures, while Major Adams was our simulated Federation Commander of the Beta Cetti defence force. For this scenario Lowig had theoretical access to any units in the Imperial Military, that have somehow assembled and jumped without Federation spies noticing, so our sneak attack has, to use the vernacular, caught them with their pants down”

Colonel Lowig: Yes sir. To simplify things we assumed that all craft assembled and departed from Starven, given the fleet a unified arrival point and time which will be the simulation T0 point. Using our latest intelligence reports on the colony defences, I used standard force depletion of an interstellar fleet fighting a static defence of 3:1 numerical multiplier when selecting my units.

Fleet Admiral Wilbur: So I see, looking at your force listing you have included the 67th Fusiliers, good to see my old boys getting in the mix.

Colonel Lowig: Yes sir. Orbital fighting experience for assaulting the main hab. Nasty business there.

Fleet Admiral Wilbur: Indeed, you know my nephew is a captain in the 67th so you would be putting him deliberately into a very bloody fight.

Colonel Lowig: Err, no sir….

Fleet Admiral Wilbur: Would be a capital idea. The boy is a strutting peacock in his uniform but never done any proper soldiering. Combat would do him a galaxy of good. Now Colonel you just said that you went for a 3:1 force multiplier, but my maths shows that while you may have that in troops, you have at least 5:1 in naval assets against the planetary defence force.

Colonel Lowig: Yes sir. It will become clear in a moment. The fleet departs Starven on date T-20, the arrival point will allow them to reach the planet with 30 hours of maximum burn on the capital ships and 34 hours on the troop transports

Fleet Admiral Wilbur: 30 hours? What is the arrival calculation of that distance to the planet?

Colonel Lowig: 90% of ships pull the piste no problem. 9.5% are unable to form a gradient. 0.5% will form a gradient but it will collapse mid flight. Failures biased to the heavier ships.

Fleet Admiral Wilbur: so we are playing the odds for racking up casualties before the first shot is fired, biased towards your most powerful vessels As for the other 10%, if I remember my maths correctly, adding the time to form another gradient with an additional distance they need to be from the planet will probably be about 6 hours behind the rest of the fleet for the purposes of planetfall give or take?”

Colonel Lowig: Correct sir.

Fleet Admiral Wilbur: So off we fly for gold and glory. Major Adams. I suspect this is the point when you come in.

Major Adams: Yes sir. My tachyon detection net picked up the fleet at T-5. I did the maths and concluded that this must be a massive enemy fleet and immediately squark to all other planets in system and dispatched my fastest courier ships to request reinforcements. We estimate that my reinforcements start arriving from the closest worlds at T-2.

Fleet Admiral Wilbur: So 2 days before we have even made system fall. By the time we arrive I see that the colonels force multiplier has dropped to 3.5:1.

Colonel Lowig: Yes sir. On arrival the fleet immediately begins a maximum burn acceleration towards the planet. Arrival time of T1.25-1.5

Major Adams: Meanwhile my second wave of reinforcements arrive, and as they know they will not reach planetfall before the imperial fleet they instead aim to arrive behind them to set up pincer action.”

Fleet Admiral Wilbur: So we all play race to the planet, at which point we engage the planetary defence grid.

Colonel Lowig: Yes sir. … … … Conservative estimate is that by the time the Majors 2nd wave of reinforcements arrive we will have suffered approximately 40% loss from the capital ships, 20% on troop ships. Their system defence fleet will have been completely neutralised with the remaining FTL ships attempting to flee, the majority of the orbital weapons platforms and smaller defence stations will have been destroyed. The major orbital structures will still be intact… … … and still under Federation control.

Fleet Admiral Wilbur: And then with the largest enemy structures still shooting at you and blocking your ability to launch a ground campaign the majors fleet hits you in the back, where all your troop transports are.

Colonel Lowig: Yes sir. In our simulation from this point I emerged victorious over her forces. 40% of the major orbital structures were captured, the rest had to be destroyed. … …. …. …. … Naval losses were 60% with a further 25% suffering damage to their ardanium plating, stranding them. Federation fleet losses were in the 80% range before retreating.

Fleet Admiral Wilbur: You kept your fleet in it for a long time major

Major Adams: Yes Sir. I choose to prolong the fight and suffer the casualties in order to destroy more troop transports to prevent a ground invasion and focus on damaging the ardanium plates.

Fleet Admiral Wilbur: ah ha. And I note from these projections that you Colonel do not have sufficient troops remaining to invade sufficient key locations to gain control of the entire planet.

Colonel Lowig: … …. ….

Fleet Admiral Wilbur: No spare me the rest, I can work out what happens next, and the Majors strategy, it’s going to be textbook. She had the luxury of sending off more messengers At T 0.5 when she knew the size, location and dispossession of your forces. She would send a another messenger after that planetary engagement with an update of what happened. Based on our intelligence of average location, patrol distance and readiness, a proper Federation taskforce will arrive in system within a week that will join with her remaining ships and counterattack. At this point you would before forced to abandon any ship that couldn’t be repaired and retreat.

Colonel Lowig: … …. … All correct sir.

Fleet Admiral Wilbur: I am aware Colonel that I am considered old fashioned and ‘fusty’, but in my day one of the defining characteristics of a sneak attack was that you caught the enemy by surprise. Not give them a week to prepare a welcome for you!”