Instrument ratings for all pilots were introduced in 1950. Pilots were rated on their instrument flying ability and awarded, in ascending order, White, Green or Master Green cards. Pilots were assessed through flight tests and ground examinations, with trainee pilots required to hold at least a White card.
Instrument flying was important for flying in low visibility conditions, such as through cloud. Therefore the instrument rating scheme, still in use today, helped improve pilot safety and enabled the RAF to operate in all weather conditions.