[Stig Jarlevik]

Adriano

The Fleet Air Arm started to adapt side numbers (codes) as an easy means of identification already in 1923.
The system developed over the years and the of course the most famous and most photographed ones were those during the 1930s (actually begun during 1934-36)
These three digits were applied in a system, ie
001-099: Catapult aircraft
102- : Fighters (strangely 101 was not used)
501- : Fleet reconnaissance
601- : Fleet Spotter reconnaissance
As in all systems there were plenty of exceptions to the above, meaning that a side code did not necessarily have to fit in...

Oddly enough it did not last long and already in 1937-38 it was slowly being replaced by a new system which was complete around 1939 where you had initially a letter and digit followed by another letter, ie A1A, A1B where the last letter stood for the individual aircraft. Running out of single letters ensured a two letter system-digit-letter came into use, ie AA4A etc

To answer your questions
1 - 3: They were all fighters
4: Is more difficult to answer since the same aircraft types were recoded. To take No 800 Sq as an example, they used Nimrods and Ospreys when formed in May 1933 coded 501-510 (Nimrods) and 208-210 (Ospreys). In May 1936 the Nimrods received new side numbers 102-109, while the Ospreys received 123-125

If you are very interested I can recommend the Air Britain book The Squadrons and Units of the FAA by Theo Ballance, Lee Howard and Ray Sturivant. A real gold mine

Cheers
Stig