Battle of Britain WI: All Spitfires in 11 Group

An arguable fact was that Spitfires weren't good escorts.

It may well be that the Spitfires weren't escorts at all, Fighter Command devised a tactic to utilise the Defiants turret guns to maximum effect by mixing types in their patrols. Sometimes Spitfires and Defiants, sometimes Hurricanes and Defiants, sometimes all three. German aircraft flying above the patrol would assume from a distance that the patrol consisted of purely single seat fighters, dive down from above and behind and get picked off by the unexpected turret guns. This tactic saw it's greatest moment on 29th May in the skies above Dunkirk when in a mixed formation of all three types where 264 Squadron "claimed" to have destroyed 7 Bf109s and 10 Bf110s on a single patrol plus 2 Ju87 destroyed. A later patrol that day saw 264 Squadron claim a further 20 German aircraft shot down, mainly Ju87s.
 
It may well be that the Spitfires weren't escorts at all,

Indeed, they weren't, but they were referred as such, officially or not. There was no RAF doctrine for using fighters as escorts for bombers, so there wouldn't be such for "fighters" either. By 1941, bombers got escorts, but then they were just bait. Whirlwinds were talked of as being escort fighters, but ended up dragging Spitfires with them as their escorts. It's all just semantics, and talk's cheap.
 
Is this the kind of thing you were thinking of??

Defiant production is to be stopped after the first run of 87 aircraft is completed, expected to be at the end of May, thereafter production is to be switched to Spitfires with production levels expected to reach 25 in July and 30 each month from that point onwards. The two existing Defiant squadrons, 264 and 141, are to be converted to Spitfires and will become operational no later than the third week of July.This will require each squadron to be supplied with a single flight of Spitfires for working up, 12 aircraft in total, with further aircraft supplied from the beginning of July as and when available until they reach an established figure of 16 aircraft per squadron prior to becoming operational.
In addition all available Spitfire squadrons are to be transferred to 11 Group as soon as possible and before 8th July, the date set for the creation of 10 Group.In order for this to occur each squadron must be brought up to full strength in the number of aircraft or at least on a par with the squadron it is to replace.Squadron rotation will begin on 1st July with the order of rotation at the discretion of AOC Fighter Command.

The Minister for Aircraft Production has assured The Air Ministry that with the additional production of Spitfires from the Castle Bromwich site and from the switch of production from the Defiant to the Spitfire that it will be possible to keep all spitfire squadrons supplied through the coming months.

Additional production levels are expected to reach the following:


  • May – 10
  • June – 13
  • July – 39
  • August – 49
  • September – 55
  • October – 69
It is expected that there will be 61 Spitfires in storage awaiting delivery to the
squadrons by the end of June 1940.
Note: The figure of 61 is based on the assumption that there was OTL 50 ready Spitfires plus additional production minus the 12 aircraft required for conversion of Defiant Squadrons to Spitfires.
50+10+13-12 = 61 Spitfires available for issue to the Squadrons.
RAF Fighter Command Order of Battle, 1st July 1940 (From Appendix II, The Most Dangerous Enemy)

11 Group

Sector A Tangmere
43 Squadron – Tangmere, 13 Hurricanes, 18 Pilots
145 Squadron – Tangmere, 11 Hurricanes, 17 Pilots
601 Squadron – Tangmere, 15 Hurricanes, 19 Pilots
FIU – Tangmere, 4 Blenheims, 10 Pilots
Sector B Kenley
64 Squadron – Kenley, 10 Spitfires, 19 Pilots
615 Squadron – Kenley, 12 Hurricanes, 21 Pilots
111 Squadron – Croydon, 12 Hurricanes, 17 Pilots
501 Squadron – Croydon, 10 Hurricanes, 18 Pilots
Sector C Biggin Hill
32 Sqaudron – Biggin Hill, 12 Hurricanes, 16 Pilots
79 Squadron – Biggin Hill, 12 Hurricanes, 14 Pilots
245 Squadron – Hawkinge, 15 Hurricanes, 16 Pilots
610 Squadron – Gravesend, 14 Spitfires, 20 Pilots
600 Squadron – Manston, 8 Blenheims, 22 Pilots
Sector D Hornchurch
65 Squadron – Hornchurch, 11 Spitfires, 16 Pilots
74 Squadron – Hornchurch, 10 Spitfires, 20 Pilots
54 Squadron – Rochford, 12 Spitfires, 18 Pilots
Sector E North Weald
56 Squadron – North Weald, 16 Hurricanes, 20 Pilots
151 Squadron – North Weald, 14 Hurricanes, 20 Pilots
85 Squadron – Martlesham, 15 Hurricanes, 21 Pilots
25 Squadron – Martlesham, 6 Blenheims, 22 Pilots
Sector F Debden
17 Squadron – Debden, 14 Hurricanes, 19 Pilots
Sector W Filton
92 Squadron – Pembrey, 11 Spitfires, 19 Pilots
213 Squadron – 14 Hurricanes, 20 Pilots
234 Squadron – 9 Spitfires, 21 Pilots
Sector Y Middle Wallop
238 Squadron – Middle Wallop, 10 Hurricanes, 17 Pilots
236 Squadron – Middle Wallop, 11 Blenheims, 19 Pilots
Sector Z Northolt
1 Squadron – Northolt, 10 Hurricanes, 18 Pilots
609 Squadron – Northolt, 15 Spitfires, 18 Pilots
604 Squadron – Northolt, 10 Blenheims, 21 Pilots
257 Squadron – Hendon, 13 Hurricanes, 17 Pilots
Note: Hurricane Strength To be replaced = 163 in 13 Squadrons or 12.5 per Squadron (Considering each squadron should have 16 aircraft at full strength that gives a 28% Serviceability rate)

12 Group

Sector G Duxford
19 Squadron – Fowlmere, 9 Spitfires, 25 Pilots
Sector J Coltishall
242 Squadron – Coltishall, 11 Hurricanes, 25 Pilots
66 Squadron – Coltishall, 12 Spitfires, 26 Pilots
Sector K Wittering
229 Squadron – Wittering, 14 Hurricanes, 20 Pilots
266 Squadron – Wittering, 8 Spitfires, 21 Pilots
23 Squadron – Colly Weston, 10 Blenheims, 20 Pilots
Sector L Digby
46 Squadron – Digby, 15 Hurricanes, 17 Pilots
611 Squadron – Digby, 3 Spitfires, 21 Pilots
29 Squadron – Digby, 10 Blenheims, 15 Pilots
Sector M Kirton
222 Squadron – Kirton, 14 Spitfires, 16 Pilots
264 Squadron – Kirton, 12 Defiants, 21 Pilots (Changed to Spitfires, 6 on strength)
Church Fenton
73 Squadron – Church Fenton, 8 Hurricanes, 22 Pilots
87 Squadron – Church Fenton, 14 Hurricanes, 23 Pilots
616 Squadron – Church Fenton, 11 Spitfires, 19 Pilots
249 Squadron – Leconfield, 10 Hurricanes, 23 Pilots
13 Group

Catterick
41 Squadron – Catterick, 11 Spitfires, 21 Pilots
219 Squadron – Catterick, 10 Blenheims, 19 Pilots
Usworth
607 Squadron – Usworth, 10 Hurricanes, 17 Pilots
72 Squadron – Acklington, 12 Spitfires, 19 Pilots
152 Squadron – Acklington, 8 Spitfires, 25 Pilots
Turnhouse
253 Squadron – Turnhouse, 13 Hurricanes, 19 Pilots
603 Squadron – Turnhouse, 10 Spitfires, 19 Pilots
141 Squadron – Turnhouse, 14 Defiants, 20 Pilots (Changed to Spitfires, 6 on strength)
605 Squadron – Drem, 8 Hurricanes, 17 Pilots
602 Squadron – Drem, 10 Spitfires, 23 Pilots
Dyce
263 Squadron – Grangemouth, 3 Hurricanes, 7 Pilots
Wick
3 Squadron – 12 Hurricanes, 18 Pilots
504 Squadron – 12 Hurricanes, 15 Pilots
Note: From 1st July to 9th July a total of 18 Spitfires were lost and required replacement, 12 as per OTL plus 6 as a result of the swap (8 Hurricanes lost in 11 Group = 6 Spitfires).In addition 8 Spitfires were allocated to 264 and 141 Squadrons.

By the morning of 10th July 11 Groups Order of Battle is as follows; the strengthening of squadrons to bring them to a similar level of readiness to those replaced in 11 Group required the issue of a further 35 aircraft.

By the 10th July ready replacements of Spitfire aircraft had risen to 66.

Sector A Tangmere
FIU – Tangmere , 4 Blenheims
72 Squadron – Tangmere, 12 Spitfires; Moved from Acklington on 2nd July to replace 145 Squadron
602 Squadron – Tangmere, 13 Spitfires; Move from Drem on 4th July to replace 43 Squadron
152 Squadron – Tangmere, 12 Spitfires; Moved from Acklington on 7th July to replace 601 Squadron
Sector B Kenley
222 Squadron – Croydon, 14 Spitfires; Moved from Kirton on 1st July to replace 501 Squadron
616 Squadron – Croydon, 13 Spitfires; Moved from Church Fenton on 3rd July to replace 111 Squadron
92 Squadron – Kenley, 13 Spitfires; Moved from Pembrey on 2nd July to replace 615 Squadron
64 Squadron – Kenley, 10 Spitfires
Sector C Biggin Hill
41 Squadron – Biggin Hill, 13 Spitfires; Moved from Catterick on 3rd July to replace 32 Squadron
610 Squadron – Biggin Hill, 14 Spitfires; Moved from Gravesend to Biggin Hill on 2nd July
604 Squadron – Gravesend, 10 Blenheims; Moved from Northolt to Gravesend on 4th July
611 Squadron – Hawkinge, 12 Spitfires; Moved from Digby on 8th July to replace 245 Squadron
603 Squadron – Hawkinge, 13 Spitfires; Moved from Turnhouse on 4th July to replace 79 Squadron, moved directly to Hawkinge rather than Biggin Hill
600 Squadron – Manston, 8 Blenheims
Sector D Hornchurch
65 Squadron – Hornchurch, 11 Spitfires
74 Squadron – Hornchurch, 10 Spitfires
54 Squadron – Rochford, 12 Spitfires
Sector E North Weald
25 Squadron – Martlesham, 6 Blenheims
85 Squadron – Martlesham, 15 Hurricanes
19 Squadron – North Weald, 12 Spitfires; Moved from Fowlmere on 5th July to replace 151 Squadron
56 Squadron – North Weald, 16 Hurricanes
Sector F Debden
266 Squadron – Debden, 12 Spitfires; Moved from Wittering on 6th July to replace 17 Squadron
Sector Z Northolt
234 Squadron – Northolt, 12 Spitfires; Moved from St Eval on 5th July to replace 257 Squadron, moved directly to Northolt rather than Hendon
66 Squadron – Northolt, 12 Spitfires; Moved from Coltishall on 1st July to replace 1 Squadron
609 Squadron – Northolt, 15 Spitfires
Thorney Island
236 Squadron – Thorney Island, 11 Blenheims; Moved from Middle Wallop on 4th July
 
Defiant production is to be stopped after the first run of 87 aircraft is completed, expected to be at the end of May, thereafter production is to be switched to Spitfires with production levels expected to reach 25 in July and 30 each month from that point onwards.

That would be amazing if a factory could go from buildinging one type of their own design at the rate of less than one a day to building an utterly different design by another company at the rate of 1 a day in 60 days.
 
That would be amazing if a factory could go from buildinging one type of their own design at the rate of less than one a day to building an utterly different design by another company at the rate of 1 a day in 60 days.

Yep I know, although it would have been 1.25 Defiants per day, but its the only way to get to what is being asked for... and don't forget the Supermarine technical staff are trying to sort out the mess at Castle Bromwich a month earlier than OTL as well while all this is going on.
 
Note: The figure of 61 is based on the assumption that there was OTL 50 ready Spitfires plus additional production minus the 12 aircraft required for conversion of Defiant Squadrons to Spitfires.
50+10+13-12 = 61 Spitfires available for issue to the Squadrons.
RAF Fighter Command Order of Battle, 1st July 1940 (From Appendix II, The Most Dangerous Enemy)

11 Group

Sector A Tangmere
43 Squadron – Tangmere, 13 Hurricanes, 18 Pilots
145 Squadron – Tangmere, 11 Hurricanes, 17 Pilots
601 Squadron – Tangmere, 15 Hurricanes, 19 Pilots
FIU – Tangmere, 4 Blenheims, 10 Pilots
Sector B Kenley
64 Squadron – Kenley, 10 Spitfires, 19 Pilots
615 Squadron – Kenley, 12 Hurricanes, 21 Pilots
111 Squadron – Croydon, 12 Hurricanes, 17 Pilots
501 Squadron – Croydon, 10 Hurricanes, 18 Pilots
Sector C Biggin Hill
32 Sqaudron – Biggin Hill, 12 Hurricanes, 16 Pilots
79 Squadron – Biggin Hill, 12 Hurricanes, 14 Pilots
245 Squadron – Hawkinge, 15 Hurricanes, 16 Pilots
610 Squadron – Gravesend, 14 Spitfires, 20 Pilots
600 Squadron – Manston, 8 Blenheims, 22 Pilots
Sector D Hornchurch
65 Squadron – Hornchurch, 11 Spitfires, 16 Pilots
74 Squadron – Hornchurch, 10 Spitfires, 20 Pilots
54 Squadron – Rochford, 12 Spitfires, 18 Pilots
Sector E North Weald
56 Squadron – North Weald, 16 Hurricanes, 20 Pilots
151 Squadron – North Weald, 14 Hurricanes, 20 Pilots
85 Squadron – Martlesham, 15 Hurricanes, 21 Pilots
25 Squadron – Martlesham, 6 Blenheims, 22 Pilots
Sector F Debden
17 Squadron – Debden, 14 Hurricanes, 19 Pilots
Sector W Filton
92 Squadron – Pembrey, 11 Spitfires, 19 Pilots
213 Squadron – 14 Hurricanes, 20 Pilots
234 Squadron – 9 Spitfires, 21 Pilots
Sector Y Middle Wallop
238 Squadron – Middle Wallop, 10 Hurricanes, 17 Pilots
236 Squadron – Middle Wallop, 11 Blenheims, 19 Pilots
Sector Z Northolt
1 Squadron – Northolt, 10 Hurricanes, 18 Pilots
609 Squadron – Northolt, 15 Spitfires, 18 Pilots
604 Squadron – Northolt, 10 Blenheims, 21 Pilots
257 Squadron – Hendon, 13 Hurricanes, 17 Pilots
Note: Hurricane Strength To be replaced = 163 in 13 Squadrons or 12.5 per Squadron (Considering each squadron should have 16 aircraft at full strength that gives a 28% Serviceability rate)

12 Group

Sector G Duxford
19 Squadron – Fowlmere, 9 Spitfires, 25 Pilots
Sector J Coltishall
242 Squadron – Coltishall, 11 Hurricanes, 25 Pilots
66 Squadron – Coltishall, 12 Spitfires, 26 Pilots
Sector K Wittering
229 Squadron – Wittering, 14 Hurricanes, 20 Pilots
266 Squadron – Wittering, 8 Spitfires, 21 Pilots
23 Squadron – Colly Weston, 10 Blenheims, 20 Pilots
Sector L Digby
46 Squadron – Digby, 15 Hurricanes, 17 Pilots
611 Squadron – Digby, 3 Spitfires, 21 Pilots
29 Squadron – Digby, 10 Blenheims, 15 Pilots
Sector M Kirton
222 Squadron – Kirton, 14 Spitfires, 16 Pilots
264 Squadron – Kirton, 12 Defiants, 21 Pilots (Changed to Spitfires, 6 on strength)
Church Fenton
73 Squadron – Church Fenton, 8 Hurricanes, 22 Pilots
87 Squadron – Church Fenton, 14 Hurricanes, 23 Pilots
616 Squadron – Church Fenton, 11 Spitfires, 19 Pilots
249 Squadron – Leconfield, 10 Hurricanes, 23 Pilots
13 Group

Catterick
41 Squadron – Catterick, 11 Spitfires, 21 Pilots
219 Squadron – Catterick, 10 Blenheims, 19 Pilots
Usworth
607 Squadron – Usworth, 10 Hurricanes, 17 Pilots
72 Squadron – Acklington, 12 Spitfires, 19 Pilots
152 Squadron – Acklington, 8 Spitfires, 25 Pilots
Turnhouse
253 Squadron – Turnhouse, 13 Hurricanes, 19 Pilots
603 Squadron – Turnhouse, 10 Spitfires, 19 Pilots
141 Squadron – Turnhouse, 14 Defiants, 20 Pilots (Changed to Spitfires, 6 on strength)
605 Squadron – Drem, 8 Hurricanes, 17 Pilots
602 Squadron – Drem, 10 Spitfires, 23 Pilots
Dyce
263 Squadron – Grangemouth, 3 Hurricanes, 7 Pilots
Wick
3 Squadron – 12 Hurricanes, 18 Pilots
504 Squadron – 12 Hurricanes, 15 Pilots
Note: From 1st July to 9th July a total of 18 Spitfires were lost and required replacement, 12 as per OTL plus 6 as a result of the swap (8 Hurricanes lost in 11 Group = 6 Spitfires).In addition 8 Spitfires were allocated to 264 and 141 Squadrons.

By the morning of 10th July 11 Groups Order of Battle is as follows; the strengthening of squadrons to bring them to a similar level of readiness to those replaced in 11 Group required the issue of a further 35 aircraft.

By the 10th July ready replacements of Spitfire aircraft had risen to 66.

Sector A Tangmere
FIU – Tangmere , 4 Blenheims
72 Squadron – Tangmere, 12 Spitfires; Moved from Acklington on 2nd July to replace 145 Squadron
602 Squadron – Tangmere, 13 Spitfires; Move from Drem on 4th July to replace 43 Squadron
152 Squadron – Tangmere, 12 Spitfires; Moved from Acklington on 7th July to replace 601 Squadron
Sector B Kenley
222 Squadron – Croydon, 14 Spitfires; Moved from Kirton on 1st July to replace 501 Squadron
616 Squadron – Croydon, 13 Spitfires; Moved from Church Fenton on 3rd July to replace 111 Squadron
92 Squadron – Kenley, 13 Spitfires; Moved from Pembrey on 2nd July to replace 615 Squadron
64 Squadron – Kenley, 10 Spitfires
Sector C Biggin Hill
41 Squadron – Biggin Hill, 13 Spitfires; Moved from Catterick on 3rd July to replace 32 Squadron
610 Squadron – Biggin Hill, 14 Spitfires; Moved from Gravesend to Biggin Hill on 2nd July
604 Squadron – Gravesend, 10 Blenheims; Moved from Northolt to Gravesend on 4th July
611 Squadron – Hawkinge, 12 Spitfires; Moved from Digby on 8th July to replace 245 Squadron
603 Squadron – Hawkinge, 13 Spitfires; Moved from Turnhouse on 4th July to replace 79 Squadron, moved directly to Hawkinge rather than Biggin Hill
600 Squadron – Manston, 8 Blenheims
Sector D Hornchurch
65 Squadron – Hornchurch, 11 Spitfires
74 Squadron – Hornchurch, 10 Spitfires
54 Squadron – Rochford, 12 Spitfires
Sector E North Weald
25 Squadron – Martlesham, 6 Blenheims
85 Squadron – Martlesham, 15 Hurricanes
19 Squadron – North Weald, 12 Spitfires; Moved from Fowlmere on 5th July to replace 151 Squadron
56 Squadron – North Weald, 16 Hurricanes
Sector F Debden
266 Squadron – Debden, 12 Spitfires; Moved from Wittering on 6th July to replace 17 Squadron
Sector Z Northolt
234 Squadron – Northolt, 12 Spitfires; Moved from St Eval on 5th July to replace 257 Squadron, moved directly to Northolt rather than Hendon
66 Squadron – Northolt, 12 Spitfires; Moved from Coltishall on 1st July to replace 1 Squadron
609 Squadron – Northolt, 15 Spitfires
Thorney Island
236 Squadron – Thorney Island, 11 Blenheims; Moved from Middle Wallop on 4th July
Bravo.:cool: I nominate you to replace Portal.;)
 
If its of any use the number of Defiants delivered to 01.07.40 was 108 and by 15.10.40 the total had increased to 267.

The total number of Spitfires delivered at these dates was 909 and 1,426 respectively.

And for Lysanders it was 618 and 756. Of the latter total 106 had gone overseas and 3 sent to Finland.
 
I was just wondering about the names involved, rather than the numbers. Dowding was the man who removed the Defiant from daytime operations following 141 Squadron's debacle, but he hadn't the power or the will to cancel production. Shortly after, Salmond and Freeman are going to suggest the use of Hurricanes as night fighters, a task at which Defiants were better equipped, and which they would no longer be able to perform if production is halted. Is Britain going to cancel its best night fighter on the eve of its pre-eminence? And what is the man's name? Forget that Britain's best hope for an effective target tug is going down the drain as well. Being able to hit a target is pretty near as important in battle as anything else. I am reminded of the Westland Whirlwind's first encounter with an enemy aircraft. Two Whirlys with closely grouped powerful 20 mm cannon encounter a Ju-88 and the result is one damaged Ju-88. It seems like target tugs, and their use, are perhaps more important than weight of fire, in at least that instance. Meanwhile, Westlands at Yeovil did take some of the pressure off Spitfire production after the Woolston bombings, being involved in the very involved Spitfire sub-contracting production, but they weren't able to establish production nearly as quick as we would have Boulton Paul.

While we're at it, who is the man who determines that 11 Group should be maximum Spitfires? Certainly not Churchill. He was always amazed and underwhelmed that his "modern fighters" always performed poorly in the Med, North Africa and Far East. Or maybe it is.
 
I was just wondering about the names involved, rather than the numbers. Dowding was the man who removed the Defiant from daytime operations following 141 Squadron's debacle, but he hadn't the power or the will to cancel production. Shortly after, Salmond and Freeman are going to suggest the use of Hurricanes as night fighters, a task at which Defiants were better equipped, and which they would no longer be able to perform if production is halted. Is Britain going to cancel its best night fighter on the eve of its pre-eminence? And what is the man's name? Forget that Britain's best hope for an effective target tug is going down the drain as well. Being able to hit a target is pretty near as important in battle as anything else. I am reminded of the Westland Whirlwind's first encounter with an enemy aircraft. Two Whirlys with closely grouped powerful 20 mm cannon encounter a Ju-88 and the result is one damaged Ju-88. It seems like target tugs, and their use, are perhaps more important than weight of fire, in at least that instance. Meanwhile, Westlands at Yeovil did take some of the pressure off Spitfire production after the Woolston bombings, being involved in the very involved Spitfire sub-contracting production, but they weren't able to establish production nearly as quick as we would have Boulton Paul.

While we're at it, who is the man who determines that 11 Group should be maximum Spitfires? Certainly not Churchill. He was always amazed and underwhelmed that his "modern fighters" always performed poorly in the Med, North Africa and Far East. Or maybe it is.

No matter how far fetched it seems, to get these changes to occur it needs only two men; Dowding and Lord Beaverbrook. The debate over the Defiant's effectiveness as a day fighter had been on the boil for months. As the result of a discussion between the two, Beaverbrook promised increased Spitfire production, Dowding took him at his word, devised the plan to have all Spitfires moved to 11 Group and the fate of the Defiant was sealed as the production line was needed for Spitfires. Beaverbrook had complete autonomy over aircraft production, no involvement from the War Cabinet or Air Ministry required, what he said happened.

As for target tugs, I think that's a bit of a red herring, the first of 140 Defiant TTs was produced in early 1942, they could have been replaced very easily by other types such as the Battle.
 
It would probably take months for Boulton-Paul to change from Spitfire to Defiant production.

The company did build a Defiant with 8 forward firing machine guns and no turret. In an emergency it would probably have been quicker to put that into production instead of switching to Spitfires.
 
It would probably take months for Boulton-Paul to change from Spitfire to Defiant production.

The company did build a Defiant with 8 forward firing machine guns and no turret. In an emergency it would probably have been quicker to put that into production instead of switching to Spitfires.

I agree - the P.94 was a viable aircraft, quick to build with the same tools and jigs in place, indeed I think BP had a double production line so maybe both could have been done at the same time,
Very little needed to be done with the change over, extra time and modification to get the guns in the wings together with the ammo feeds, easy enough to fare over the turret hole. If anything once its set up the single-seat version could be made faster than the original.
In OTl, the proposal, was probably made to late, made earlier, or the question put to B-P rather than the other way around, it may have been different.
 
IIRC For the P.94 it was necessary to remove at least one of the Defiant's wing tanks, which were outboard of the undercarriage and replace it with a fuselage tank on the centre of gravity. A little more than just adding the guns! Though the design work already done for both the P.88a and the P88b could well have made it easier to fit four 20mm cannons, if they had been available. Now if the combat limitations of the Defiant had become apparent earlier (say by new year 1940) than such a change might well have been made in time to have such aircraft in service by the end of the BoB. Whilst not really capable of dogfighting with a 109, their four 20mm cannons would certainly do more to bring down bombers than the eight RCMG then carried by the Spitfire and Hurricane.
 
All right, I'll amend 'very little' to 'not a lot':

- instead of routing the fuel lines to the wings, they are routed to the mid-fuselage where the new fuel tank will be,
- establish supplies of suitable fuel tanks, fit in-place connect lines to fuel pump & carb on engine, install and connect up fuel filler cap & hose to the tank,
- fit the armament to the wings - OTL offered 12 x 0.303" or 4 x 20 mm cannon, suspect for commonality 8 x 0.303" would be installed.

Still, no big deal, compared to starting from scratch - apart from the engine & prop.
 
I've got my copy of Aircraft for the Few by M.J.F. Bowyer out and it has a photograph of K8310 the first Defiant prototype after it was modified to single-seat fighter configuration.

The text says that twelve Browning machine guns or 4 cannon could have been fitted and that Boulton Paul claimed a maximum speed of 345mph with a Merlin XX engine. The second cockpit could have been retained for an AI radar operator.

Boulton Paul also proposed Defiant developments with Griffon or similarly powerful engines mounting six 20mm cannon in the wings, plus the turret or an observer.

Unfortunately it doesn't say when K8310 first few in the modified configuration.

However, it does say that the Defiant Mk II with the Merlin XX producing 1,260hp which flew on 20th July 1940 was only 12mph faster than its predecessor which had a Merlin I producing 1,030hp.
 
Dare I suggest proposals for a 1-seat Defiant are getting rather far afield from the OP?:)

The original OP stumbles on the fact that not enough Spitfires were produced within the timeframe to make the proposition viable. To argue a solution, one has to understand why the Spitfire was slow coming into production at Supermarine Woolston and all the reason why Castle Bromwich was slow coming on line, as well as how Spitfires were actually manufactured. When the Woolston plant was bombed, Spitfire production was only delayed about a week, because Spitfires were made in many many places. Some of those places were critical, and weren't bombed at all. One of those places, Pressed Steel Company, was built by Morris and the American Budd Company, of Budd Conestoga fame, although they sold out before too long. They possessed the large powerful presses required for the wing leading edges, the metal sheeting of which required special tooling from the rolling mill to provide the material. These leading edges were joined to the special spars made at Reynolds Tubing, and fitted to some ribs made by Westlands to manufacture the torsion box which was the main structure of the Spitfire wing.

Duplicating these companies and their equipment and workforce would have made doubling production a snap. Establishing another assembly plant would not. After the Woolston bombing, the work continued in bus depots and such. Rather than fall back on Boulton Paul to aid production, it might be foresightful to cancel Lysander and Whirlwind production and rely on Westlands Yeovil to boost production, since they were involved in wing production already, and would be a source of production in the future anyway, particularly with Seafires. The original role for Lysanders was a bust, and Rolls Royce had already screwed the Whirlwind from ever being viable.

With regard to who won the Battle of Britain, the Pressed Steel Company site now assembles BMW Minis.
 
I know this has raised a few questions about Spitfire production, cancelled production runs of other aircraft etc. but it's still an interesting question of What If 11 Group had all Spitfire squadrons regardless of how the increase in Spitfire production is achieved.

I'm currently working on this very question based on the increases I've already mentioned, ie Castle Bromwich improvements and Boulton Paul switching from Defiant to Spitfire no matter how unlikely these events are. I want to see what the effect of an increase in production would be and what kind of level of increase would be needed to sustain an all Spitfire 11 Group.

Currently busy with real world stuff though unfortunately but I'll get back to it as soon as possible ;)
 
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