Creating a new Space Marine Chapter is not an easy thing. Strangely, perhaps the simplest stage is the agonisingly long and difficult process of compiling the gene seeds necessary for such an endeavour. Whilst each Astartes Chapter is obligated to regularly send genetic samples to the Adeptus Mechanicus, in part for this very purpose, the Space Marines are proud and aloof, and above all independent in the way that only they can afford to be. Even when they deign to pay their tithes, each seed must be exhaustively studied to ensure it is free of mutation or other taint, a process which the material itself does not invariably (or even often) survive intact. Finally (though least problematically), the genetic stockpiles must be sorted by Primarch.
These, however, are simply issues of time and of patience. Eventually sufficient gene-seed will be available for the creation of one thousand new Space Marine warriors. It is at this point that things become truly difficult.
It is not always true that savage martial prowess precludes discipline, but the inverse correlation is sufficiently high to be a genuine problem. Taking a thousand feral tribesmen or Deathworld survivors and turning them all into super-human killing machines is all very well, but the end result is not an army, it is a mob; a terrifyingly destructive mob that has only ever known killing, and is delighted to have suddenly become so much better at it.
Thus, the new recruits must be tempered, guided in the best way to do their duty, taught to see their fellows as brothers in arms, rather than rivals, meals or even, occasionally, clothing. Added to this problem is the fact that persuading the initiates to undergo the honour in the first place is next to impossible, unless other Space Marines are the ones doing the "persuading". The martial societies (to the extent to which the latter term is appropriate) that provide the best raw material also tend to resist having the concept of the Adeptus Astartes explained to them by Imperial Missionaries or clanking Tech Adepts.
The only solution is to attach a number of more experienced Space Marines to the nascent Chapter. This is not even remotely as easy as it sounds. There exist no force in the Imperium less willing to see themselves as part of a whole than an Astartes Chapter. A Catachan would mutter threats of violence were he forced to join a regiment of Drookians, a Battle Sister would likely refuse point-blank to change from one Order to another, no matter who issued the command. A Space Marine's response, however, is not one that bears thinking about. The history of the Imperium contains all too many references to Chapters allowing themselves to become extinct rather than retreat, or join with other Chapters. The colours of a marine's Chapter is a source of almost psychotic pride. It is fortunate indeed that Foundings are so rare an occurrence, for finding the necessary genetic material is child's play compared to locating enough Space Marines to form an Officer's Corps for a new Chapter. This was the dilemma faced during the Twenty-Fourth founding in M38.
In the case of the Krakens of Greyjoy salvation came from the remnants of the very Chapter they had been created to replace. The fleet-borne Emperor's Shields Chapter, already severely under-strength following Waaagh! Dedtoof, found themselves under attack from the Apostles Of Minthras Traitor Chapter whilst in the final stages of regrouping their fleet at Raxos. Only a single Thunderhawk Gunship, carrying thirty battle brothers, escaped the resulting conflagration, either through carelessness on the part of the Apostles, or perhaps as a deliberate humiliation.
Most of those Marines who survived wished to attempt to board and repair the nearest intact escort vessel and follow the Apostles' fleet to their base, before attempting to gain their revenge there. Brother-Captain Rekasson, however, who now held the sorrowful distinction of being the the Chapter's most senior officer, realised that such an action would be simple folly. If they were to gain their revenge, it could not be on such unfavourable terms. If he was to join his brothers in death, he had no intention of telling them that they were unavenged. When the Adeptus Mechanicus offered Rekasson and his band of warriors an entire Chapter, raised from the savage inhabitants of the world of Four Feathers, he realised that he would have his instrument of vengeance, and that the Apostle's days were numbered. Thus did Brother-Captain Rekasson of the Emperor's Shields become Chapter Master Rekasson of the Krakens of Greyjoy, and the long tale of the Space Squids begin.