The 411 On Chain Drives

I can't seem to find a valid resource for chain driven vehicles, much less in the Land Rover Defender 90 Series.  I am ignorant as to why the chain drive is more powerfull and why it is unique amongst it's class. Could someone throw a link this way or explain which Land Rover vehicles do/don't have the chain drive, and how it effects speed, off-road abilities, torque, power, reliability, and service.
 
Thanks,
Addison