Editing Thunder Warriors (section)

===Development===
The Emperor could have simply made custom augmentations for each Regiment/Legion of Thunder Warriors to specialize them for each intended purpose and could have used the knowledge from the Mechanicum and cybernetics to correct the genetic flaws and smooth things out. Considering that this was how he ended up with twenty Astartes Legions, then why not bring both programs together and create Thunder Warriors with added organs so they could adapt to different environments, or make Astartes with greater size, strength, and resilience on a par with the warriors that preceded them? Considering his development of Primarchs, Astartes, and Custodes, he clearly had enough knowledge, and skill, and tools to do this, whether it was cost effective or not is a different matter; as Constantin Valdor once mentioned that to make an army of Custodians on a similar scale to the Thunder Warriors would have practically bankrupted Terra, and who knows if the programs were even compatible with each other? The existence of the World Eater Blackshield - Endryd Haar, the Terran Iron Hand - Autek Mor, as well as Arik Taranis’ success in splicing Astartes gene-seed into his body to stabilize his lifespan also suggests that it is possible that the Thunder Warriors could’ve been “upgraded and repurposed” as senior advisory cadres to supplement the Astartes but the rebellion and the cost to do so before Luna and Mars were subjugated was too prohibitive and moot if they had to be purged after the Palace Coup. Even then, it would’ve been imperfect in the same manner Khor Phaeron, Amon, and Luther weren’t able to truly fit into their adopted legions as augmented adult humans; particularly when Endryd Haar was still a berserker (albeit, an intelligent one, as Malcador remarked) without the Butcher’s Nails and killed any subordinates who defied his orders. On the flipside, Autek Mor was a sociopath tactician who didn’t give a damn about collateral damage to non-combatants or even his own subordinates so long as all his enemies wound up dead.

In any case: As much as people try to put the blame squarely at his feet for being lazy or short-sighted; Amar Astarte claimed that while his influence certainly sped things along, ''the Emperor'' was not the only person working on his transhuman projects. He had enormous laboratories with hundreds, if not thousands of scientists working in secrecy just to get as far as they did with the Space Marines, and had been working on the Space Marine project even '''before''' the Thunder Warriors existed; they were only ever just a stop-gap. Bearing in mind that the project was set-back and all of the laboratories were destroyed '''twice'''. First with the Scattering of the Primarchs due to the fucking moron [[Erda]] dropping the anti Chaos God defenses to protect the Primarchs (which would severely backfire), secondly when Amar Astarte herself decided that the loss of said Primarchs was going to doom the Astartes Program to the same failures as the Thunder Warriors ''- a very telling reason indeed-'' This means the Great Crusade race was essentially started early, as the Emperor was now on a timer in order to reclaim them before they were irretrievable and still needed to build the [[Astronomican]], claim [[Mars]] and get ''himself'' out into the galaxy to meet his sons. And he had to do this all before the Orks and/or the Rangdan hit critical mass and killed everything so Big E was already under massive pressure.

The fact that [[Primaris Marines]] now exist that are larger, stronger, and more resilient than basic Space Marines shows that the gap has finally been filled. They are still not the equals of Custodians on the tabletop, but we're only talking the about the level of variance within a single point. They are probably much closer to Thunder Warriors and are potentially what the Emperor always intended, if he had the time to focus on his project and continue, or at the very least just one or two steps below, Thunder Warrior level fighters with all the stability and mass production capability of Astartes.

Considering the threats to Unity and dangers of Terra at the time; From nations of psykers to Men of Iron hidden within the core of the planet, and [[Chaos]] licking their lips the whole time, let alone everything else like the [[Rangdan Xenocides|Rangda]] and [[Ork]]s hitting critical mass and bulldozing everything. It's unsurprising the Emperor moved as quickly as he did and used every tool at his disposal.