Sorry Sixpence but I notice I had made an error in the above reply which I have gone back and edit it to correct it.
Minimum requirements ?
Headquarter placed as Bishop and set as Zone 1
Field placed for Bishop and set as Zone 1 master
Headquarter placed as Knight and set as Zone 1
Field placed for Knight and set as Zone 1 master
Headquarter placed as Rook and set as Zone 1
Field placed for Rook and set as Zone 1 master
I should have been
Headquarter placed as Bishop and set as Zone 1
Field placed for Bishop and set as Zone 1 master
Headquarter placed as Knight and set as Zone 2
Field placed for Knight and set as Zone 2 master
Headquarter placed as Rook and set as Zone 3
Field placed for Rook and set as Zone 3 master
I'm just tired tonight
Pokie