Recently I have undertaken the task of running a Deathwatch one-shot whose plot is very simple:
An ancient and very special Land Raider that was in the hands of the Tech-Priests on some far flung world or other. They had it because they were deep in meditation over its secrets. Then some detestable Xeno wave (probably Orcs just to keep everything nice and easy) showed up and overwhelmed the garrison on that world and they called for help.
Because that Land Raider is so special, the call went to the Deathwatch - that Land Raider MUST be recovered! Not only because it is a priceless and irreplaceable artifact, but also because of precisely why it is special.
It is special because it was one of a series of vehicles that were used to experiment on hooking up a pilot directly to the control interfaces - the same way they do with Dreadnoughts. Of course that technology was lost, indeed all the means to direct-hook a pilot to the vehicle was lost except for the method used in Dreadnoughts.
So, the Land Raider is very old, and it contains the still living but slumbering body of a very old Space Marine. And that's why it's special and must be recovered.
What do you think? Any thoughts? Any pointers?