ok so this is it so far
Origins of the Dragoons
They were a late 18th, early 19th founding chapter, they were setting out from Sol with an almighty crusade fleet to investigate the Vincies Subsector to hunt Orks, Eldar pirates and to ensure the Emperors words were carried to the far reaches of the galaxy. It consisted of a brand new Space Marine fleet and they had close support from an Imperial Navy detachment. It was an entire Adeptus Astrates Chapter including all of its support, a fleet of materials, ammo and spares to help the chapter found a Homeworld and a detachment of the Adeptus Mechanicus to safe guard their investment.
By the time of their arrival the fleet had grown to include an entire battle group of the Imperial Navy and Guard, a Blood Angels strike force, an Inquisitor, a regiment of the Adeptus Mechanicus Skittari and a local Rogue Trader. On arrival to the sector they sent out scouts to investigate systems that the Rogue Trader had visited and more importantly ones which he (OOOOH MAYBE A SHE) had avoided. One of these systems reported a mass of automated defences and tech which the escorts could not approach. After the fleet had made the system safe the Mechanicus ships set about scanning neighbouring systems and investigating the wrecks of the system. This system appeared to be a long abandoned and overlooked Adeptus Mechanicus outpost from the time of the age of strife or before.
Now it seemed that the whole system was abandoned and the Adeptus fleet while not wanting to leave, the marines also were dissuaded against leaving. Therefore it was decided that the fleet should set up base in the outer rims of the system while the Mechanicus investigated more and looked for any STCs that may be there.
After two months the Astrates and accompanying Imperial Navy and Guard commanders were getting weary of being couped up bored in a system in a barely defendable system. On threatening to leave the Mechanicus suddenly discovered how to reactivate the sentry guns, to the downfall of a couple of escorts sat too close. Several neighbouring systems appeared to be habitable so the fleet divided up into strike forces to investigate any possible life on these planets and bring the systems back into the fold.
These systems consisted of several dead worlds, but more importantly several worlds that may have, at a time before the age of strife and the warp storms, supplied the system the Mechanicum were so interested in with raw materials, man power and supplies. On this the fleet set out hunting down the pirates and renegades surrounding the immediate area.
The Chapter Master of the Emperors Lancers had a massive fleet, millions of tons of resources and potentially a forge world to help him with his crusade. With this knowledge he decided to create a home world on one of the Hive Worlds within one of the most heavily inhabited systems.
The Imperial Guard acted as temporary PDF while a sufficient force was trained and outfitted. The Blood Angels set of on missions mainly against the Orks while the Emperors Lancers expanded their territory and set about the Eldar and Pirates in surrounding systems.
hope it looks good, please be nice and ill explain all that i may of missed or mucked up
by the way i haven't decided on a name for them yet