In my opinion this would not be possible with a withdrawal north of London whether it is as far as Debden or as an interim withdrawal to North Weald.
There are a few things people seem to forget, ignore or are unaware of regarding the 'Dowding System'
So in summary if you continue without a withdrawal Fighter Command would still be able to counter most raids in the south and south east although the strength of 11 Group would degrade and it may take many months to recover. If you withdraw to Debden/Duxford/Middle Wallop you can no longer counter all raids and those that you do intercept you will have a much small force available. In my opinion you will have given the Luftwaffe air supremacy over the critical invasion area in the south and south east of England and in doing that you're inviting invasion.
- Each sector, due to technical reasons, could only control a maximum of 4 squadrons at a time. 11 Group with 7 sectors could operate a maximum of 28 squadrons at any one time. In reality there were only ever 23 squadrons at most so there was always going to be some redundancy. If, however, Biggin, Kenley and Honchurch were abandoned you are automatically reducing the number of squadrons by at least 7 that can be operated by 11 Group. If you withdraw further then this number reduces significantly. There are probably workarounds to this but would add complications that would undoubtedly reduce the effectiveness of the system.
- The HF R/T's used to stay in contact with the squadrons had an effective range of 60 miles meaning that control beyond 60 miles from the operations room was not always possible. VHF sets were being fitted that increased this range to 100 miles but these were few and far between.
- Typical first response of Fighter Command was to put squadrons in the air once it was obvious a raid was inbound. This meant scrambling squadrons and setting patrol lines for those squadrons to fly to until it became more obvious where the Luftwaffe were targeting. Patrol lines included Maidstone to Canterbury or Tonbridge to Ashford. In this way a Spitfire Squadron from Kenley, for example, could be in the Maidstone area at 20,000ft within 17 minutes waiting to be given their final vector (A Hurricane squadron would take a little longer). If all went well such a squadron would be in the area just before the approaching enemy formation. Other squadrons would be vectored when ready whilst further squadrons would be sent to patrol airfields. In this way 31% of scrambles resulted in contact with the enemy, this was compared to only 10% contact rates for standing patrols.
- As mentioned above a Spitfire squadron at immediate readiness (i.e. Pilots in the cockpit ready to go) took 17 minutes to start-up, taxi, take off, assemble and climb to 20,000ft. The distance covered during this time would be approximately 35 miles. A Hurricane squadron would take 20 minutes to climb to the same height and would cover a distance of 40 miles (the Spitfires would now be at 50 miles). Within 20 minutes a bomber formation of He111s could reach Ashford or Canterbury, a formation of Ju88s a little further, easy enough to intercept from Kenley, Biggin Hill or Hornchurch and their satellites and forward bases. From North Weald a Spitfire squadron would get to Ashford just in time, a Hurricane Squadron would not, and neither would be able to counter a raid further south of Ashford. From Debden the Germans would be able to roam freely anywhere south of Maidstone.
The idea that Fighter Command can swoop down from the north en-masse, I believe, isn't realistic. The Luftwaffe can get in and out of the area unmolested, Fighter Command don't have the communication range or technical ability to control such formations so reliance would be on luck and standing patrols only.
A most succinct and well reasoned explanation of why Fighter Command could not retreat. I think several of us were groping towards that point. Great post!!