Prior to the Mountbatten Report (1960's/ early 70's), the Prison Service only had the following Uniformed Grades; OFFICER, PRINCIPAL OFFICER (2 BARS), CHIEF OFFICER 2 (CROWN), CHIEF OFFICER 1 (CROWN & PIPS).
The Mountbatten Report recommended the introduction of the SENIOR OFFICER Grade and the insignia became;
OFFICER, SENIOR OFFICER (1 PIP & Red insert behind cap badge), PRINCIPAL OFFICER (2 PIPS & Orange insert behind cap badge), CHIEF OFFICERS remained the same, The Prison Auxiliary Grade was also introduced or was already in service which was not responsible for inmates with the Letter A on their epaulettes.
Uniforms were also changed from black to what was known as London Transport Blue/Grey. (It appears that LT Bus Drivers refused to wear the new Blue/Grey two piece jackets and trousers in a similar material to Barrack Dress trousers and the uniforms were issued to Prison officers). Rank worn on collars of jackets.
In Long Kesh in the 70's, you had various different type and colours of uniforms depending where the Prison Officer was detached duty from, England & Wales, NI and Scotland.
Fast forward to 1987 and FRESH START. Black uniforms were back in, Prison Auxiliaries were made responsible for inmates and changed their epaulettes from letter A to a blue stripe.
Hats with slashed peaks were also discouraged as they were to military!!!! and eventually ceased being worn on the landings.
Then comes PRIVATISATION/CIVILISATION/MARKET TESTING, ranks are changed on the HMP Officers to coloured bars on epaulettes and the rank of Principal Officer is dropped and that grade are made Managers and put in suits. Then the Rank of Principal Officer is returned back into Uniform and the Senior Officer grade is getting the chop.
Change for the sake of change.