Aircraftman
Aircraftman (AC) or aircraftwoman (ACW) is the lowest rank in the British Royal Air Force (RAF) and the air forces of several other Commonwealth countries.
Aircraftman ranks below leading aircraftman and has a NATO rank code of OR-1. It is now a training rank only and no airmen in productive service hold this rank. Aircraftmen do not wear any rank insignia.
The rank was introduced on the formation of the RAF in 1918, replacing the Royal Flying Corps rank of air mechanic 2nd class. There were two grades: Aircraftman 1st class (AC1) and aircraftman 2nd class (AC2; also colloquially known as an "AC plonk").
In RAF slang, aircraftmen are sometimes called "erks".
In the Royal Canadian Air Force, the rank is known as "aviator". This was changed from private in spring 2015 when the RCAF changed the colour of its rank insignia from gold to pearl grey. It is the lowest rank in the RCAF. Prior to 1968 the rank of aircraftman was used in the RCAF as in other Commonwealth air forces.
The Royal Australian Air Force also uses both aircraftman and aircraftwoman.
In the Royal New Zealand Air Force, the rank is known as "aircraftman", regardless of the person's sex, in line with "seaman" in the Royal New Zealand Navy.
...
Wikipedia