Originally Posted by
ROC man
Great grandfather who served in RFC was issued with 13*** in November 1915 which was carried forward into RAF service in April 1918.
Likewise for my Grandfather, RNAS Air Mechanic (F 22***) who appears to have retained that number on 1 Apr 18 on transfer to the RAF.
Slightly surprised by his uniform with peaked cap, as a basic Naval Rating ... he was only a newly-joined Air Mechanic 2nd Class when that photo was taken. But Google has helped explain that ... Class III was worn by RNAS ratings!
https://www.uniform-reference.net/in..._1.html#class1
Called the "fore-and-aft rig" in contrast to the "square rig," Class III uniform was similar to Class I, but without gilt buttons and with badges worn on the sleeves. Black buttons were worn on blue uniforms and white on white uniforms. The cap badge was embroidered in red thread. The personnel distinction reflected in Class III dress originated with those known as "idlers" in the sailing navy, who did most of their work during daytime hours and did not keep watch around the clock. Class III was worn by petty officers and lower ranks of the Shipwright, Accountant, Medical and Naval Police ratings, as well as those of the Royal Naval Air Service.