= System Defense Tactics
As with defensive warrens [see article on warren design] the main objective of a naval force defending a star system is to deny its use to an invader. In practice, if faced by a superior invading force, the defending admiral’s role is usually to buy time for orbiting defense platforms to irradiate or otherwise destroy the worlds they orbited.
In the Tranquility system, for example, the main asset was the planet Tranquility and its moons. There was considerable value, too, in the asteroid belts and the moons of outer planets, but these were thinly distributed.
History does hand us exceptions. Some planets have been taken by insurrection, deception, or civil war. And the human Marines of Tranquility were taught stirring stories — possibly fabricated — of defending forces who had held out against a besieging enemy for decades until a relieving battle fleet arrived in system and lifted the siege.
The main defense position around Tranquility was a zone of hollowed out asteroids towed into a perimeter that bulged out around the planet and in a higher orbit around the sun. About 30-50 million klicks farther out, to be precise. Fast response squadrons of warboats were stationed within the perimeter, and around fortified bases elsewhere in the star system.
The generals of old Earth knew that a key to victory for an attacker the ability to launch an assault at the place and time of her choosing, and achieve superiority in numbers or firepower at her chosen point. Of course, defending generals knew this and would stretch every effort to frustrate the attacker’s plans.
Out in space, even the near space around a single star, the battlefield is so utterly vast that the attacker seems to have unlimited options in choosing where to mass her forces. For a squadron to put a defensive shell around a star, at about the same diameter as Tranquility’s orbit, would require each ship to be tens of millions of klicks away from its nearest neighbor.
The key to defending a star system is not a front line so much as a combination of rapid-response reserves with a vast and highly sensitive sensor sphere. This sphere would detect an attacking force far enough out into interstellar space for the mobile defensive forces to mass in response. The scale needed to create an effective sensor sphere big enough to defend an entire star system is too immense for human contemplation. The numbers are so enormous that they become abstract.
Nonetheless, with star systems typically held for tens of thousands of years before being abandoned, these kinds of sensor spheres are commonplace.
The timescales mean also that enemies can flood the system with nanoscale spybots in advance of an invasion. With the defender’s dispositions known, the invader has merely to select an appropriately superior force for the invasion to be a success.
This relative ease with which an attacker, working over a long time period, can take enemy star systems (or, at least, cause the defender to destroy her own assets) leads many wars to take on a tit-for-tat character.
If you destroy my star system, I will destroy yours.
A slow sequence of destruction plays our over decades, centuries or longer, until one side loses the will or resource ability to have any more of their planets destroyed.