Yeah it's a bit confusing. As far as efficiencies go:
You need three of a specific CHASSIS (ie: hunchback, centurion, atlas) to unlock all ELITE efficiencies.
You need three of a specific CLASS to unlock ELITE efficiencies on a mech (ie: three MEDIUM, three HEAVY, three LIGHT) and unlock MASTER and double basic.
The short version is this: to get the basic, you need three Ravens. Once you get the three ravens through all the basic, you need three LIGHTS that have finished all basics to progress through elite to master.
EXAMPLE: I have three light class chasses: Jenner, Commando, and Raven. I have to get three commandoes, three jenners, and three ravens to unlock the elite masteries on all three chasses. At this point I can choose three mechs: like, one jenner, one raven, one commando, to take thru the elite masteries. You need the LIGHT mechs to allow for total unlock of the couble basic/master upgrades. I needed three of each chassis thru basic, but only three of each LIGHT to unlock master and double efficiencies.
I'm a little drunk ATM, but I think that made sense. GL, HF, and kill lots of griefers.
Edited by Hammerfinn, 24 August 2013 - 11:53 PM.