I`ve just watched the eposode it's called A Day Out, But the officer is actually a Chief Officer II they have a Crown but also 2 Bars like mr mackay is this correct or a mistake by the BBC. There's also a Chief Officer II in the first seen of Edisode 1 New Faces, old Hands with the same insignia a Crown and 2 Bars, So I guess Chief Officer I Pre mountbatten report Would have had a Crown, Pip and 2 bars, still not sure about the Rank Grade 4, Assistant Chief officer don`t know if the rank existed pre mountbatten or was it introduced the same time as senior officer, suppose it would make sense 1 pip for a senior officer 2 for a principal officer and 3 for Assistant Chief officer.