Interestingly, at the time of the March 1939 planning memo calling for 100 octane to be brought into use by 16 squadrons, 15 squadrons were operational with Spitfires or Hurricanes, with 3 others in the process of forming or converting. The units are as follows:
Mar-39
Sqdn Base Aircraft
1 Tangmere Hurricane
19 Duxford Spitfire
32 Biggin Hill Hurricane
41 Catterick Spitfire
43 Tangmere Hurricane
46 Digby Hurricane Converting from Gauntlets March 39
54 Hornchurch Spitfire Converting from Gladiator March 39
56 North Weald Hurricane
66 Duxford Spitfire
73 Digby Hurricane
74 Hornchurch Spitfire
79 Biggin Hill Hurricane
85 Debden Hurricane
87 Debden Hurricane
111 Northolt Hurricane
151 North Weald Hurricane
213 Wittering Hurricane
501 Filton Hurricane Forming with Hurricanes in March 39
The status of other squadrons that had not converted to Hurricane or Spitfire by March 1939 but had converted by December 1939, when the stations at which they were based in December 1939 were required to be supplied with 100 octane, were as follows:
3 Kenley Gladiator
17 Kenley Gauntlet
65 Church Fenton Blenheim
72 Church Fenton Gladiator
152 not formed none
504 Hucknall Gauntlet
602 Abbotsinch Gauntlet
603 Turnhouse Gladiator
607 Usworth Gladiator
609 Yeadon Gladiator
610 Wittering Hind
611 Speke Hind
615 Kenley Gauntlet
616 Kenley Gauntlet
The
100 octane approval memo from 24 September 1938 suggests that the impetus for converting to 100 octane pre-war was for improved take-off performance, given the propellers that the aircraft were equipped with at that time.