You’re welcome, Daz, for what it was worth.

On a 1941/42 operational sortie, “finger four” at a guess, 4 a/c left to right at intervals of 200 feet staggered laterally, rather less than that from the lead man (at No 2) to the rear-most, and under 100 feet between each. See eg Deighton, Fighter.

How this might translate into line astern (or whether it would at all) in action I can’t say. I’m some way out of my ground here, though my understanding was that on contact the idea was to break into pairs, each wingman sticking to his leader.

It will be very interesting to see whether 1941 edn AP129 considers action tactics like finger four, as opposed to the 1937 Air Exercise formations. I’ll await others input with great interest.

Edit: Other sources
Every so often I seem to slip into a really irritating period of obtuse forgetfulness. Age, or too tired, I guess – they do pass. So, it eventually dawns on me that the RAF Air Historical Branch Narratives may well offer an answer in the detail and as close to “the horse’s mouth” as anyone might wish. Try

AIR 41/18 The Air Defence of Great Britain Vol. 4: The Beginning of the Fighter Offensive 1940-1941

AIR 41/49 The Air Defence of Great Britain Vol. 5: The Struggle for Air Supremacy Jan 1942-May 1945

If you haven’t got access, and no-one else offers a suitable reply, let me know and I’ll consult the AWM copies. I need a trip over there shortly, I’m just starting to think out the next round of 211 Squadron writing.

Thanks for the info, Don. I think I may have been confusing myself about the formation, coupled with the fact that trying to describe or draw it out is a bit difficult.

The reason I ask is this is for a story/project that I’m working on, and I wanted to make sure of the right formation used at the time.