In order to get an idea behind why my Squat army is being built the way it is, here is a small piece of background...
We knew they were coming. We pleaded with the Imperials and they made excuse after excuse before turning their backs on us. We had fought alongside them for hundreds of years against all manner of foe... even the dreaded filth of chaos... yet that mattered not. We were cast adrift to await our fate on our home worlds.
As the tendrils of the Tyranid fleet began to infiltrate our forward bastions, we knew that our worlds were forfeit. No matter what terrible destruction our fusion batteries and magma cannons wrought upon the Tyranid fleet, the immeasurable number of living vessels continued forward.
We detonated a star to halt the incursion but it seemed to act as a beacon to them as more and more of the disfigured ships appeared in the systems around our home worlds. It was to be the doom of our kind...
... or so the Imperials thought.
Months before the aliens began their invasion, our Ark ships were stocked and ready for departure. Filled with our young, our women, our artificers and artisans, our technology and security details of strong troops. All of the provisions needed for the journey were packed in to every space before the ships left.
On the surface of the planet were the Kings and their finest warriors. Forge fathers and master tacticians; fathers and sons, mothers and daughters... prepared to bring down this alien menace or die trying. For the home world... for valour... for the yet to be written history.
Then the skies went black... filled with the spores, advance guard and pods of the Tyranid invasion force. They poured into the atmosphere and were vaporised by weapons of untold power using energy wrought from the core of the planet itself... but eventually the sheer volume of attackers silenced the guns and the ground assault began. Every corridor, every street and every room was fiercely defended but it was inevitable that the planet would fall and as the escape ships burst through the atmosphere into space, carrying the wounded and the scribes, the final act of defiance was enacted... the core was destroyed by Ion bombs, taking the planet and billions of creatures with it.
All through the home worlds the same story was being told. The Ark ships were many light years away when their planets were succumbing to their fate; the few remaining survivors blasting through the Tyranid fleet to meet up with the Arks.
And what of those survivors who had so valiantly fought to draw in the Tyranids and attempt to destroy as many as possible before escaping? There were very few... and those that survived were rent to pieces. Limbs were lost, acid burns covered their bodies, their lungs were filled with the filthy spores of their enemies. Had it not been for the Mechanicus, most of them would have succumbed to their injuries but in a pact devised between the Forge Fathers and the Mechanicus, Squat technology was traded for life support and cybernetic expertise.
The few veteran Tyranid hunters that remained were 'repaired' by the Mechanicus. Missing limbs were replaced, lungs were cleansed and artificial re-breathers were fitted. The valiant Squats left the Mechanicus forge worlds changed beyond recognition. Half Squat, half robot but filled with fire and ready to share their knowledge and battle skills with future generations of Squat warriors... the next time the Tyranids dared to take action against the Squat brotherhoods, they would not fare so well.
Once the veterans had been taken care of, the Squat fleets rendezvoused at a point of space far beyond the range of the Tyranid fleets before travelling to the only planets that they knew would accept and help them... the Abhuman worlds where the Ogryn, Ratlings and Beastmen lived. It was there that they offered their technological expertise for sanctuary and the bonds of friendship and trust were built...