Skirmish... The only true mode is extreme (or what it is called). The installment also states that.

That has to date been my only battle at that level, perhaps I should try it again, as the Empire attacked me early with about 8 squadrons of fighters against which I initially only had a single squadron of X-wings... But I won, though it wascostly and gave me the time to go for Assault Frigates (and that proved valuable.

Btw it was on the Bilbringi map (with 100k resources to start with).