So, had ideas, didn't want to try making a plan, so instead made an omake! Of ideas, and a tentative plan that might work for the first wave with accompanying rationale!
To Beat Back the Wave: The Unannotated Strategy Outline Presentation at the High Council
From the High Council Historical Records of the Imperial Trust
"The way I see it, the best option is to nip this in the bud as much as possible, even though it means forfeiting the defensive advantage of fighting over and on our better fortified worlds and creating a logistical nightmare for ourselves in keeping our armies and navy supplied so many light years from our home systems. Those problems can be mitigated through proper preparation, but a several-fold increase in size for a combat fleet that already out matches our own cannot."
"We obviously cannot come up with a full strategy without knowing how the Tyranids will respond to our attacks—if they will group up further to increase the combat power of individual hive fleets, if they do nothing and continue to follow the course they have set, if they will disperse to preserve their numbers and increase the potential biomass they can harvest, of if they do something truly unexpected—but we can outline a solid approach to the initial engagements as they enter the galaxy."
"From the size and combat power of each hive fleet, combined with how much of their losses they are capable of recovering in less than total defeat, worlds not defended by a major power in this region can feasibly do nothing more than delay the coming tide and slightly reduce the mass it gains—even if through some miracle they were capable of inflicting near total losses, after consuming the biosphere the Tyranid fleet should come out ahead. As the Shadow has also become an extremely potent interdiction tool, we cannot even use the window created by the delay to inflict harassment, let alone effective harassment given their mass reclamation abilities. As things stand the only way anyone can effectively reduce the mass of the dispersed splinter fleet is through total defeat of constituent hive fleets and the only way to prevent its growth is to prevent them from landing on worlds with rich biospheres."
"Ideally our first step should be to reduce the worlds targeted in the first wave that are inherently hostile to sane life in the galaxy to ash ourselves. Each individual planet of this type can be destroyed with minimal losses on our side with an average of two task forces in a year. Given that it is not a question of if their biospheres will be destroyed but if their biomass will feed the insatiable maw of the Great Devourer I feel there is no reason to avoid doing so to preserve habitable planets. While this will result in some losses on our side and remove any potential delays, the reduction in expected fleet strength of the Tyranids should be well worth it for future waves."
"To do this, for practical reasons we would need some degree of certainty that the major Chaos powers in the region do not interfere. A great purge of minor Chaos powers in the area with the help of the Eldar is something that could easily provoke a reaction even given their current distraction with the Waaagh, and our resupply lines will by necessity pass through areas under Chaos control."
"The best way to do this is by ensuring they discover the coming threat of the Tyranids. While it may distract them from handling the Orks, it will explain our actions in our preemptive purge and greatly reduce the odds that they will deliberately interfere at a large scale. Unfortunately smaller scale interference and attempting to steal our technological secrets is all but inevitable, but the greater threat of the Tyranids snowballing outweighs the losses on that front. It is highly likely that between the current fighting with the Orks and what Tyranid forces do hit them any followers of Chaos in a position to do so will be reduced to a shadow of their former selves regardless. It should also reduce the odds that those noticing Eldar involvement conclude that this is a region they have any special interest in, as they will have a readymade explanation for Eldar interference in protecting the galaxy from the apocalyptic threat of an exponentially growing Tyranid invasion. This should hold water even if the invasion is somehow handled relatively bloodlessly and with seemingly excessive force, as those with even a hint of rationality will likely conclude that the threat was considered severe enough that overkill was employed."
"While it is hardly the potential galactic scale threat that the Tyranids represent, we should also confirm that even with the distraction the local Chaos forces will succeed in destroying the recently formed Waaagh and figure out what we can do to influence it if they will not. Our own military is highly unlikely to be able to deal with the fallout of the Waaagh surviving, especially given the losses to the Tyranids we can expect to take."
"Ideally, the Tyranids will not retarget hivefleets aimed at worlds that have been burned of biomass to biomass containing worlds initially passed up by the fleet or redistribute the forces that were to target them to instead support the fleets hitting other worlds, but we do not know if this is the case or not. Given their very poor strategic speed speed, however, it is likely that our task groups could burn a substantial fraction of many of the worlds targeted in the first wave after the hive fleets are effectively committed to the world and escape before the Shadow prevents transit from those worlds. In this case, we should likely prioritize Ork worlds for destruction, as they stand to provide more biomass to the Hive fleet. Of course, if burning worlds even after the fleets have seperated and targeted specific worlds causes the fleets to retarget onto nearby worlds resulting in a delay with only minor effects on expected biomass gain then the cost benefit analysis of deploying our own forces to burn out the worlds would need to be re-evaluated."
"When the first wave itself hits we can meet elements of it in non hostile systems with the battlefleets we can spare from our defenses. In addition to protecting the minor powers, a laudable goal if not one we can frequently spare the forces to do, this allows for the defeat in detail of some elements of the splinter fleet before they have grown in size. Despite the strain of the distance this is likely to be our best chance to inflict a very favorable exchange ratio in our losses, as each planet consumed will increase the size of an individual hive fleet substantially requiring a similar percentage increase in the number of our own ships devoted to the fight to maintain the same loss ratio and a far greater percentage increase to maintain the same absolute loss number to defeat the hive fleet."
"As the Shadow in the Warp is not likely to prevent Webway transit, it should be possible in systems with Webway access to reduce the human forces committed and have the Eldar move from system to system, applying overwhelming force to shatter the hive fleets and having the human forces run cleanup. While this would require the human forces in system to play a delaying action while somewhat understrength before the Eldar arrive, overall it should allow for both greater coverage and improved loss ratios, so long as the forces are capable of avoiding major losses before the Eldar can arrive. While the Shadow would ordinarily prevent effective communication for coordination and timing between the different systems in question, between the Divinatory skills available to the forces and the fact that a relay system for messages using the Webway should be both fast and possible, as each system in question is by necessity connected to the Webway, the required level of coordination should be feasible."
"Should we ultimately decided to run a major campaign like that described here, we should also consider creating a base of operations to ease resupply and repair as those are likely to be major issues. One possibility on that front would be to convert an orbital city into a functional forward operating base and place it in the region, ideally in dark space and near a Webway gate. By having repair facilities and an at least moderately secure location for convoys to create a stockpile, logistical constraints should be greatly eased—although if the degree would be worth the cost and disruption it would cause is debatable."
"Finally, there is the question of the local Necrons. While direct cooperation with them is out of the question due to the hostility between them and the Eldar as well as the conflicts with Dragon's Nest, it is undoubtable that they have a vested interest in preventing the Tyranids from gaining a foothold in this galaxy and would take steps to cull them even if they are not in the direct path of this splinter fleet. Unfortunately, it is very difficult to say what, if any, measures they would take—anything from meeting them in open battle in the Void to preemptively sterilizing all the worlds they are targeting while waiting for reinforcements is possible. I would like to suggest we consider providing them with the information we have about the Tyranid splinter fleet and whatever tentative plan we have for it, though, simply because warning them increases the odds that they are aware of and respond to the threat, reducing our own expected losses in handling it, and so that we do not accidentally work at cross purposes, such as by having both fleets show up to target a single hive fleet or by the Necrons choosing to sterilize a world we were going to protect. I would also like to note it is quite possible that they are aware of this splinter fleet already, too, and without hearing we had and would devote the forces needed to protect some of the uncorrupted sane worlds in the path would instead sterilize them simply to deny the Tyranids the biomass."
