It was definitely 65 or 66. I was at Gaydon from Jan 65 to Mar 66 and acquired my prefix while I was there, probably around mid 65. I was summoned to General Office and given a slip of paper with my new prefix on it. My apprentice number of 6 digits (688xxx) was prefixed with R0 (zero) so all numbers were padded out to 8 digits. Later after commissioning the letter migrated to the end, but not the zero.
Last edited by EngAl; 29th Sep 2020 at 18:29.
Reason: typo