Mustang Origins (1 Viewer)
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P-51B Mustang: North American's Bastard Stepchild that Saved the Eighth Air Force, by James William "Bill" Marshall & Lowell F. Ford an interesting book that I have just started reading.
It appears that the birth of the Mustang (as originally named, before it became the P-51) is quite a complicated saga. The book explains that the initial requirements issued to North American Aviation by the British Purchasing Commission were those of RAF Specification F.18/39 which, in turn was based on (British) Air Ministry Operational Requirement OR.73.
1. By reference to "The British Aircraft Specifications File, British Military and Commercial Aircraft Specifications 1920-1949", by KJ Meekcomms and EB Morgan it appears that F.18/39 was not issued until several months after the date mentioned in Marshall & Ford's book; and again by reference to the Meekcomms & Morgan book, it appears that F.18/39 was written specifically to cover the all-British Martin Baker MB.3 fighter. Is there any particular 'proof' that F.18/39 was issued to NAA and that it was used to formulate a brief; or could it be that once the Mustang details were finalised it did look as if it would fit F.18/39?
2. Does anyone have a full copy of F.18/39 that can be shared?
3. Both books mentioned above state that F.18/39 was based on OR.73. Does anyone have a full copy of OR.73 that can be shared?
4. Marshall & Ford state that the in-house reference number for what would become the Mustang was NA.73 and that this number was in turn derived from OR.73, whereas every other source I have read simply lists 73 as being the next sequential design number for North American Aviation. Is there a definitive (accessible) list of NAA designs to show how NA.73 fits in?
It appears that the birth of the Mustang (as originally named, before it became the P-51) is quite a complicated saga. The book explains that the initial requirements issued to North American Aviation by the British Purchasing Commission were those of RAF Specification F.18/39 which, in turn was based on (British) Air Ministry Operational Requirement OR.73.
1. By reference to "The British Aircraft Specifications File, British Military and Commercial Aircraft Specifications 1920-1949", by KJ Meekcomms and EB Morgan it appears that F.18/39 was not issued until several months after the date mentioned in Marshall & Ford's book; and again by reference to the Meekcomms & Morgan book, it appears that F.18/39 was written specifically to cover the all-British Martin Baker MB.3 fighter. Is there any particular 'proof' that F.18/39 was issued to NAA and that it was used to formulate a brief; or could it be that once the Mustang details were finalised it did look as if it would fit F.18/39?
2. Does anyone have a full copy of F.18/39 that can be shared?
3. Both books mentioned above state that F.18/39 was based on OR.73. Does anyone have a full copy of OR.73 that can be shared?
4. Marshall & Ford state that the in-house reference number for what would become the Mustang was NA.73 and that this number was in turn derived from OR.73, whereas every other source I have read simply lists 73 as being the next sequential design number for North American Aviation. Is there a definitive (accessible) list of NAA designs to show how NA.73 fits in?
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As far as I am aware, the NA.73 was a private venture not officially to any spec.. :- F.18/39 was linked to the MB.3 and MB.5
| F.18/39 | Fighter – Hurricane/Spitfire replacement | Martin-Baker M.B.3, Martin-Baker M.B.5 |
Shortround6
Lieutenant General
The usual story is that the British approached NA to build Curtiss P-40s under license. At this time Curtiss themselves had not built a production P-40 and would not do so for several months. Curtiss could make about 80 planes a month (Hawk 75s) and was planning a large expansion of plant to meet the US and French orders. The British would not actually place an order for the P-40 until later.
There was in Nov 1939 a British Purchasing Commission which was quickly changed to the Anglo-French Purchasing Commission. This was supposed to reduce or eliminate the scramble of WW I when the British and French bid against each other and locked up production of certain factories for themselves and at times, locked the US out. You can only expand production so much.
I have no idea what NA actually had for drawings/calculations sitting in drawers, other can answer that better than I can. But the guys at NA told the British that they could design a better plane than the P-40 and do it in the famous 120 days (or after a bit of negotiation?). P-40 airframe was over 4 years old at the time (Hawk 75) and since NA would have to build/convert factory space anyway, a 4-month delay was not really that bad.
The Hawk 75, Hawk 81 and Mustang were not built to any British requirement. They were what the French and British could get quickly. In some cases the French were cleaning out the American junk drawers and when France collapsed the British just took over all existing orders.
Now for NA to get the initial 320 plane order (May 29th 1940) they had to promise something better than the P-40. They had paper, Curtiss had the XP-40 flying for over a year and has 11 P-40s flying at the factory.
Things get complicated quickly. Curtiss themselves were working on the Hawk 87 (Kittihawk) and the XP-46 fighter in late 1939 but delivery was months behind the Tomahawk series.
NA has to promise not only to beat the Tomahawk, they have to beat the proposed improved Tomahawks.
But again, they were not trying to satisfy any British requirement although they may have had them in mind.
British requirement F.18/37 called for twelve .303 guns and a speed of 400mph and lead to the Hawker Tornado, Hawker Typhoon, Supermarine Type 324, Supermarine Type 325.
The Hawker Tornado first flew in Oct 1939. How much NA knew I don't know but 6-8 .303 guns would not have been looked at with favor.
There was in Nov 1939 a British Purchasing Commission which was quickly changed to the Anglo-French Purchasing Commission. This was supposed to reduce or eliminate the scramble of WW I when the British and French bid against each other and locked up production of certain factories for themselves and at times, locked the US out. You can only expand production so much.
I have no idea what NA actually had for drawings/calculations sitting in drawers, other can answer that better than I can. But the guys at NA told the British that they could design a better plane than the P-40 and do it in the famous 120 days (or after a bit of negotiation?). P-40 airframe was over 4 years old at the time (Hawk 75) and since NA would have to build/convert factory space anyway, a 4-month delay was not really that bad.
The Hawk 75, Hawk 81 and Mustang were not built to any British requirement. They were what the French and British could get quickly. In some cases the French were cleaning out the American junk drawers and when France collapsed the British just took over all existing orders.
Now for NA to get the initial 320 plane order (May 29th 1940) they had to promise something better than the P-40. They had paper, Curtiss had the XP-40 flying for over a year and has 11 P-40s flying at the factory.
Things get complicated quickly. Curtiss themselves were working on the Hawk 87 (Kittihawk) and the XP-46 fighter in late 1939 but delivery was months behind the Tomahawk series.
NA has to promise not only to beat the Tomahawk, they have to beat the proposed improved Tomahawks.
But again, they were not trying to satisfy any British requirement although they may have had them in mind.
British requirement F.18/37 called for twelve .303 guns and a speed of 400mph and lead to the Hawker Tornado, Hawker Typhoon, Supermarine Type 324, Supermarine Type 325.
The Hawker Tornado first flew in Oct 1939. How much NA knew I don't know but 6-8 .303 guns would not have been looked at with favor.
Geoffrey Sinclair
Staff Sergeant
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A summary of F.18/39, which was issued over year before the discussions with North American
1 May 1939, Single seat fighter, File Number S.51584/RDT1 issued 4 May 1939 to Martin Baker for type MB.3 (later MBT.4 and 5).
To meet Operational Requirement OR.73, a high speed single seat fighter capable of operating in any part of the world is required as a replacement for the Spitfire and Hurricane. The outstanding requirement is to obtain the greatest possible supremacy in maximum speed over the contemporary bomber. There may be advantages to be twin engine design which would be acceptable, provided the performance was superior to that which would be obtained from a single engine aeroplane. The AUM of an aircraft built to this specification is 12,000 pounds.
Performance: The speed at 15,000 must not be less than 400 mph with the 37.V/12 engine and it is essential that the engine selected should be equipped with a two speed supercharger so that speeds below 15,000 feet may be as high as possible. The normal fuel load is to be sufficient for 15 minutes flying at maximum engine speed for take off conditions, plus 2 hours at the most economical cruising air speed at 15,000 feet plus 15 minutes at 15,000 feet at maximum engine speed for level flight at 15,000 feet, plus 30% reserve.
Engine: The aircraft shall be designed to accommodate a 37.V/12 engine but a Rolls-Royce RM.2SM engine is to be installed in the first instance.
Strength: The design requirements of AP.970, any corrigenda thereto and all current ADMs applicable to TV class acceptances are to be satisfied at 1.1 times the AUW in the fully loaded condition at the factors give for "other than experimental aeroplanes".
Armament: Two cannon guns in each wing set to fire along the line of flight, with at least 1 drum of 60 rounds of ammunition per gun. Provision shall be made for the installation of a reflector gun sight and a head sight and a Cine Camera gun, mounted internally. Protection for the pilot against armour piercing 0.303 inch ammunition is required to cover a forward cone with an angle of 20 degrees to the thrust line of the aircraft.
Wireless: TR.9D or TR.1133.
Note the Spitfire I and Hurricane, after deducting 15 minutes fuel for take off, had endurances at economic cruise of 3.1and 3.4 hours, for the Spitfire that means around 22 gallons to fulfill the combat allowance and reserves requirements of F.18/39, The MB.3 is quoted as having 120 gallons of fuel for its 2,00 HP engine compared with 84 gallons for the 1,00 HP engine in the Spitfire I.
Digital Archive – Aircraft Production Lists North American Aviation Charge Numbers (XLS format)
66 Harvard
67 XB-28
68 n/a
69 P-64
70 n/a
71 Venezuela order for AT-6 accepted in June 1940
72 Brazil order for BC-1A
73 Mustang
74 AT-6
75 Harvard
1 May 1939, Single seat fighter, File Number S.51584/RDT1 issued 4 May 1939 to Martin Baker for type MB.3 (later MBT.4 and 5).
To meet Operational Requirement OR.73, a high speed single seat fighter capable of operating in any part of the world is required as a replacement for the Spitfire and Hurricane. The outstanding requirement is to obtain the greatest possible supremacy in maximum speed over the contemporary bomber. There may be advantages to be twin engine design which would be acceptable, provided the performance was superior to that which would be obtained from a single engine aeroplane. The AUM of an aircraft built to this specification is 12,000 pounds.
Performance: The speed at 15,000 must not be less than 400 mph with the 37.V/12 engine and it is essential that the engine selected should be equipped with a two speed supercharger so that speeds below 15,000 feet may be as high as possible. The normal fuel load is to be sufficient for 15 minutes flying at maximum engine speed for take off conditions, plus 2 hours at the most economical cruising air speed at 15,000 feet plus 15 minutes at 15,000 feet at maximum engine speed for level flight at 15,000 feet, plus 30% reserve.
Engine: The aircraft shall be designed to accommodate a 37.V/12 engine but a Rolls-Royce RM.2SM engine is to be installed in the first instance.
Strength: The design requirements of AP.970, any corrigenda thereto and all current ADMs applicable to TV class acceptances are to be satisfied at 1.1 times the AUW in the fully loaded condition at the factors give for "other than experimental aeroplanes".
Armament: Two cannon guns in each wing set to fire along the line of flight, with at least 1 drum of 60 rounds of ammunition per gun. Provision shall be made for the installation of a reflector gun sight and a head sight and a Cine Camera gun, mounted internally. Protection for the pilot against armour piercing 0.303 inch ammunition is required to cover a forward cone with an angle of 20 degrees to the thrust line of the aircraft.
Wireless: TR.9D or TR.1133.
Note the Spitfire I and Hurricane, after deducting 15 minutes fuel for take off, had endurances at economic cruise of 3.1and 3.4 hours, for the Spitfire that means around 22 gallons to fulfill the combat allowance and reserves requirements of F.18/39, The MB.3 is quoted as having 120 gallons of fuel for its 2,00 HP engine compared with 84 gallons for the 1,00 HP engine in the Spitfire I.
Digital Archive – Aircraft Production Lists North American Aviation Charge Numbers (XLS format)
66 Harvard
67 XB-28
68 n/a
69 P-64
70 n/a
71 Venezuela order for AT-6 accepted in June 1940
72 Brazil order for BC-1A
73 Mustang
74 AT-6
75 Harvard
macharvard
Airman 1st Class
Thanks for the link to the production lists. An incredible collection. However, there's a glitch that needs to be fixed in the NAA list. The NA-68 was the P-64; NA-69 was the A-27 and the NA-71, -72 and - 74 (Chile) were, with some minor differences, all the result of the NA-68's promotional tour of Latin America. For more information, you can check out this book: North American NA-16 Combat Variants: Macphail, Doug, Tincopa, Amaru, Arróspide, Julio: 9798410318914: Amazon.com: Books It's the third and final tome I co-authored on the NA-16 family before retiring in 2024.
As an Amazon Associate we earn from qualifying purchases.
- Thread starter
- #7
Thank you.
That table looks as if it is from Wikipedia. It doesn't mention the Mustang, but neither does any other RAF Specification. There are quite a few planes missing from that list, so I am not sure that omission of 'Mustang' from th right hand column means that F.18/39 was not relevant to the formulation of the NAA specification. Curious.
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- #8
Thank you: very helpful and informative.
The wording of F.18/39 is interesting.
The listing of NAA charge numbers seems fairly conclusive that the '73' was simply the next sequential charge number rather than anything to do with OR.73.
It would still be interesting to read OR.73.
Brilliant information: thank you
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- #9
Thank you
Senior management at North American Aviation had been looking ahead for future business opportunities for some time. As such, they sought to obtain copies of the various specifications and requirements being released to aircraft manufacturers in the USA and Europe. With the success of their sale of the Harvard I to the UK, and with the increasing potential for another war on the European continent, they in particular sought via their representatives in the UK and via the BPC, copies of relevant specifications and operational requirements being released for future RAF aircraft. For the BPC, the specifications and ORs were a good shorthand way to inform the US aircraft manufacturers of what the Air Ministry and RAF's thinking and future directions in terms of the types of aircraft they were looking for and that the US manufacturers should aspire to.
So whilst NAA had their own ideas, to some degree shaped by USAAC requirements of the time and what information they were amassing from various sources on what a single seat pursuit type fighter aircraft might require, that gave them the starting point. By the BPC then providing copies of the latest RAF Specifications and AM ORs they could provide what the RAF were looking for in terms of aircraft performance and specific attributes considered important by the RAF - and as the RAF gained operational experience in the early stages of the War, those that were now considered 'essential' eg. self-sealing fuel tanks, armour, weight and type of armament, and aircraft performance and range.
The specifications and operational requirements also gave the BPC staff, especially their technical staff, something to measure proposals being submitted by the US manufacturers against, and also as a basis too then provide feedback and suggested changes. It also gave the BPC staff in the USA a common point of reference when providing information back to the Air Ministry, RAF, etc in the UK in their communications about what US aircraft manufacturers were offering. As happened in the discussions between NAA and BPC staff in NAA's development of their proposals to meet the BPC's requirements with their own solution rather than building P-40s.
The process for the development of an Operational Requirement for a new aircraft for the RAF took place over a period of time. It could involve the release of discussion drafts to the UK based aircraft manufacturers to ascertain which manufacturers might respond to the OR when it was finalised and released, and to 'tweak' the OR in light of the feedback received from the manufacturers, changing technical requirements and the rapidly changing situation the aircraft that resulted from the OR would have to operate in (for example latest intelligence on the performance figures of potential enemy aircraft types). You also had in the mix, the Ministry of Aircraft Production and the Department of Supply, and depending on what role the intended aircraft was proposed to fill, there might also be the War Office and the Admiralty getting involved. Between early discussion drafts and release to industry, various rounds of discussion and correspondence and the final specification being released, in some cases significant change could take place in the OR that led to the final Specification. There were also instances where a new or revised OR and Specification was released to allow a particular aircraft manufacturer and a promising proposal or prototype they might have presented to the Air Ministry and RAF to be developed - often framed as 'an emerging requirement identified.....'.
To potentially find the originals of Air Ministry Operational Requirement 73 and associated deliberations and consultation leading the the eventual release of RAF specification F.18/39, you would need to dig into the surviving files in the UK Archives at Kew. But the final version of OR.73 as eventually promulgated and released to industry should underline should, be 99% the exact same technical core wording as appears in RAF Specification F.18/39. The specification as released would have the addition of some limited preamble wording introducing the requirement; and closing with some wording relating to the manner and form and timelines for industry to respond to the specification.
Those are just some quick suggestions, there may be references to other relevant original files in those files, which may not be evident by their file title - some of the policy files may not refer specifically to the OR or specification number and may be more related to the role or function proposed for the aircraft type. And large caveat, not all paperwork and files may still exist, some not considered worthy of retention in the post-war period may have been culled/destroyed. The above suggested files have not been digitised and would require either an in person visit to Kew, pre-ordering the files to view there; or arranging for and paying for the files to be copied; or having a paid researcher look in the files for you and copy the relevant parts you are interested in. The RAF Museum Hendon also holds some files and papers related to aircraft manufactured for the RAF, but that is primarily focussed on the UK aircraft manufacturers and on technical and company history type information.
In relation to the fourth dot point question in your original post, on what page do Marshall and Ford state that the OR number influenced the NAA charge number? I've read the book a number of times and don't recall that specific point.
So whilst NAA had their own ideas, to some degree shaped by USAAC requirements of the time and what information they were amassing from various sources on what a single seat pursuit type fighter aircraft might require, that gave them the starting point. By the BPC then providing copies of the latest RAF Specifications and AM ORs they could provide what the RAF were looking for in terms of aircraft performance and specific attributes considered important by the RAF - and as the RAF gained operational experience in the early stages of the War, those that were now considered 'essential' eg. self-sealing fuel tanks, armour, weight and type of armament, and aircraft performance and range.
The specifications and operational requirements also gave the BPC staff, especially their technical staff, something to measure proposals being submitted by the US manufacturers against, and also as a basis too then provide feedback and suggested changes. It also gave the BPC staff in the USA a common point of reference when providing information back to the Air Ministry, RAF, etc in the UK in their communications about what US aircraft manufacturers were offering. As happened in the discussions between NAA and BPC staff in NAA's development of their proposals to meet the BPC's requirements with their own solution rather than building P-40s.
The process for the development of an Operational Requirement for a new aircraft for the RAF took place over a period of time. It could involve the release of discussion drafts to the UK based aircraft manufacturers to ascertain which manufacturers might respond to the OR when it was finalised and released, and to 'tweak' the OR in light of the feedback received from the manufacturers, changing technical requirements and the rapidly changing situation the aircraft that resulted from the OR would have to operate in (for example latest intelligence on the performance figures of potential enemy aircraft types). You also had in the mix, the Ministry of Aircraft Production and the Department of Supply, and depending on what role the intended aircraft was proposed to fill, there might also be the War Office and the Admiralty getting involved. Between early discussion drafts and release to industry, various rounds of discussion and correspondence and the final specification being released, in some cases significant change could take place in the OR that led to the final Specification. There were also instances where a new or revised OR and Specification was released to allow a particular aircraft manufacturer and a promising proposal or prototype they might have presented to the Air Ministry and RAF to be developed - often framed as 'an emerging requirement identified.....'.
To potentially find the originals of Air Ministry Operational Requirement 73 and associated deliberations and consultation leading the the eventual release of RAF specification F.18/39, you would need to dig into the surviving files in the UK Archives at Kew. But the final version of OR.73 as eventually promulgated and released to industry should underline should, be 99% the exact same technical core wording as appears in RAF Specification F.18/39. The specification as released would have the addition of some limited preamble wording introducing the requirement; and closing with some wording relating to the manner and form and timelines for industry to respond to the specification.
Those are just some quick suggestions, there may be references to other relevant original files in those files, which may not be evident by their file title - some of the policy files may not refer specifically to the OR or specification number and may be more related to the role or function proposed for the aircraft type. And large caveat, not all paperwork and files may still exist, some not considered worthy of retention in the post-war period may have been culled/destroyed. The above suggested files have not been digitised and would require either an in person visit to Kew, pre-ordering the files to view there; or arranging for and paying for the files to be copied; or having a paid researcher look in the files for you and copy the relevant parts you are interested in. The RAF Museum Hendon also holds some files and papers related to aircraft manufactured for the RAF, but that is primarily focussed on the UK aircraft manufacturers and on technical and company history type information.
In relation to the fourth dot point question in your original post, on what page do Marshall and Ford state that the OR number influenced the NAA charge number? I've read the book a number of times and don't recall that specific point.
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- #11
Thank you: very helpful.
The reference is on page 50, at the start of the subsection titled 'NAA Chronology for January through December 1939'.
It starts: 'On January 5,1939, the BPC delivered the latest British Specification, F.18/29 Operational Requirement OR.73 to NAA….'
Apart from stating it as /29 instead of /39, the date of issue is interesting: Jan 5 1939 (or 1/5/39 in common US shorthand). From what I've read elsewhere, the date of issue was May 1 1939 (or 1/5/39 in common UK use).
Later in the same paragraph it states that this framed the requirements for what 'became the 'X73'.
They go on, on the next page, to quote requirements from 'OR.73', but don't indicate whether that is the whole text or selected bits.
On P64, towards the bottom of the page, it states that 'Charge number NA-73X was opened…' with 'all previous work on performance estimates….revised and compared against…OR.73'
(This could simply be a coincidence of numbers, but it was being suggested to me very strongly on another forum that, by reference to this book, it was clear that NAA used NA-73 because of OR.73 - further implying that OR.73 was explicitly the Air Ministry 'specification' for the Mustang and not simply for some future requirement. I'd previously read - eg in Meekcoms' book - that F.18/39 was written specifically for Martin Baker.)
Sorry if this is a wild goose chase!
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- #12
And another thing: as you can probably tell, I'm new to this forum and, indeed, this type of forum.
I can't seem to work out how to reply to a comment without including the whole of that comment in my reply: other people seem to be able to include selected parts only - how do you do that?
Okay, I've never taken any of what was written in Marshall & Ford's book as there being a correlation or conscious decision by NAA to number the NA-73 Mustang in line with OR73. I've not seen anything in that or other sources that draw any similar conclusion. Just the next NAA project number in the sequence at that time. Co-incidence, it happens.
For quotes from other users, if you don't want to quote the whole post, you can use your mouse to highlight the section of text that is most relevant to your reply. That should then bring a small pop-up that gives choices of 'quote/copy', if you select the 'quote' side of the pop-up it then saves it so when you want to start the reply you hit the insert quote, and it will drop in just the part you highlighted and selected.
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
I accidentally quoted your whole post while trying to give you an "informative" on my cellphone.
Ironic, no?
Why I try and not use my mobile/cellphone when interacting on websites like this, the danger of hitting the wrong button, unintended autocorrections, etc. Oh the irony is strong in this one!
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
I'm waiting on a desktop.
special ed
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Must be uncomfortable.
ThomasP
Chief Master Sergeant
Particularly for the desktop.
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