to their seniority in that rank provided that: (a) Chief Engine-Room Artificers, Chief Ordnance Artificers, Chief Electrical Artificers, Chief Shipwright Artificers, Chief Aircraft Artificers. Chief Mechanicians, Chief Aircraft Mechanicians and Chief Electrical Mechanicians shall rank and command over all other ratings of these eight Civil Appeal Nos. 6886-6887 of 2011 Page 6 of 9branches. "Chief" ratings within one of these branches shall rank and command between themselves according to seniority in "Chief" rating. "Chief " ratings of two or more of these branches shall rank and command between themselves by seniority as Chief Petty Officer. Where "Chief" ratings of any of these eight branches are together with Chief Petty Officers of other branches they will rank and command according to seniority as Chief Petty Officer. (b) Engine-Room Artificers, Ordnance Artificers Electrical Artificers, Shipwright Artificers and Aircraft Artificers of a particular class shall rank and command