The transmission while it appeared to be babble was reported to the higher ups who discovered something intersting.
Why? If it was babble and nothing of importance than why would a serf bother anyone with it? What possessed this serf to report this random transmission when it appeared to be nothing?
His keen danger sense alerting Valenae that something was wrong he put the entire chapter on alert and roused the full fury of the Blood Spears readying them to fight on their home soil.
So the chapter master is informed of a transmission of babble and he immediately assumes something bad is about to happen; not only that but something is about to attack the chapter homeworld? What of the chapter librarians or companies? Has he consulted them and discovered anything else to indicate such a thing?
The fortunate accidental radio transmission which caused this was the only warning of an eldar raid on the planet.
Eldar using radio transmissions? Why would a highly advanced race of psykers, who use psychic ability for damned near every aspect of their lives, resort to using something as crude as radio transmissions?
Only four days after the chapter was ordered to begin patroling the planet the eldar appeared en-masse in the skies above the planet driving the battle barges and other support craft in orbit away and wiping aside the orbital defences.
How did they just appear so close to the chapters homeworld without them knowing it? You don't just appear in the homeworld system of a space marine chapter without them knowing about it mere moments before they are on top of you. Theres an entire marines fleet on alert after all.
As this was happening he was approched alone in his study by the Eldar Farseer.
How did the farseer penetrate so far into a chapter fortress? And how did he/she know where to be in order to find the chapter master?
A fortress monestary is a heavily defended structure complete with void shields, a thing that prevents incoming fire from weapon batteries and teleportation. (Ships have to lower shields or a section of them to make teleportation possible.)
Valenae recognizing the markings of the farseer now knew exactly which of the so called Eldar "Aspects" would be fighting and prepared accordingly.
How did he recognize which aspect warriors would be present? Is this guy well trained in being able to understand eldar glyphs and symbols? And for what reason would a farseer have symbols of aspect warriors with him/her anyway?
To counter the Swooping Hawks aspect the 8th assalt company was assigned to defend the Vindicators and Whirlwinds that would be used to pummel the general infantry and Dire Avengers.
This is assuming the Eldar will be fighting to a battle plan that these marines are good at dealing with?
If the Eldar are the ones attacking a chapter homeworld, why would they be mounting anything but a highly elite surgical strike with mechanized elements protecting much of their forces? And why would swooping hawks, warriors who combat infantry and other warriors, not armour, be the ones gong after armour?
Using the 9th Devestator company to counter the Dark Reapers he believed that the battle was well in hand.
This is once again assuming the Eldar will be doing something like a straight up charge at the chapter with heavier elements providing cover to some degree. However again Eldar do not fight this way, I mean why would a dieing race not use grace and intelligence to attack their enemy and keep their own losses low over brute force and high risk of losses?
As ordered all of the available scout squads began moving quietly towards the eldar positions to discover that the Farseer was apperating from a jet bike alongside several squads of the Shining Spears aspect.
Why would the chapter master send even more scouts after learning this? And if he didn't learn this from the first group of scouts what possessed him to send more scouts from fighting to look for the other squads? If he had learned this from the first squads then why would fourth company or another company not be sent?
Valenae managed to get the 4th company onto Bikes quickly enought to counter this new threat while the scouts who discovered this and particularly the Scout Dienekes who had managed to kill one of the exarchs with his sniper rifle was inducted into the ranks of the 4th company.
Kinda seems tossed in there; we go through this whole thing and then this random scout is tossed in to be recognized as somewhat important? Perhaps he would be better served fleshed out later rather than get a line or two here.
Sorry to be seemingly ripping through your work, some things just don't make to much sense and working through that can only help your stuff to be that much better in the end.