WW2 with no Spitfire - Hurricane being primary interceptor

[CobberKane]

At the end of the BoB it was pretty obvious the Hurricane had a limited future as a front line fighter. What is less recognised these days is that there was a strong body of opinion that the spitfire too was reaching its due date. The Westland Whirlwind was seen as a strong candidate for the future of the UK's fighter force for quite a time, but at the end of the day the Spitfire proved up to the challenges of the air war as it progressed beyond 1940, whereas the Hurricane did not.
It is arguable that the BoB could have been won without the Spitfire, but to my mind it is unarguable that beyond 1940, previous heroics aside, the days of the Hurricane as a competitive front line fighter were pretty much done.

 

[nuuumannn]

I agree, Cobber. RCAFson, you are presuming that what would have happened between when the Hurricane prototype first flew and WW2 things would have been different had there been no Spitfire and this is based on what you know about WW2. Your entire argument is based on hindsight, which they did not possess when the Hurricane was being built. You have to remember that when the Hurricane first entered service it was considered the pinnacle in fighter development - the British did not know, nor could they have predicted that Willi Messerschmitt's fighter was going to be better than the Hurri Mk.I in the form of the Bf 109E, so why would the Air Staff, or Hawker insist that the Hurricane undergo drastic improvement before the war, especially since the firm was developing a replacement?

The Air Staff had such faith in the aircraft's design that the biggest British peacetime order for aircraft up to that time was placed with Hawker to build Hurricanes - 600 of them. The Langley production line was built specifically to meet the need - and because Hawker's existing facilities were little more modern than what they had been under Sopwith use in WW1 and Gloster got an order as well - this was instead of Wellingtons, that C-in-C Bomber Command Cyril Newall had hoped for. Deficiencies in its performance against the Bf 109 only became evident in the spring/summer of 1940, by then, better fighters had already flown and were being built, as mentioned earlier. Nothing would have been any different within Hawker before the outbreak of war, even if there wasn't a Spitfire.

 

[wuzak]

Hurricane development was stopped because the Spitfire existed.

The Hurricane's development was stopped because Hawker and Camm's time and effort was going towards the Tornado/Typhoon since around mid 1938.

 

[wuzak]

What is less recognised these days is that there was a strong body of opinion that the spitfire too was reaching its due date.

The F.18/37 program (Tornado/Typhoon) was to replace the Spitfire. In the end it couldn't, and its a good thing the Spitfire was around and able to be stretched, since the Typhoon was a long time coming in numbers, was unreliable for some time and certainly lacked the altitude performance of the later model Spitfires.

Who knows, if the Spitfire wasn't around the MAP may have given Supermarines a development contract for the Type 327, since some of their opposition to that aircraft was derived from their view that Supermarines took a long time turning out prototypes and even longer getting aircaft into production.

 

[merlin]

If the Hurricane was faced with the Me-109C or D, then ok it could cope but with the 'E' only just, and 'F' no way!

We know that looking back, but it was anticipated before hand:

"Early in 1937 Hawkers at Kingston started to scheme a successor to the Hurricane. They had in mind a faster and heavier armed single-engine fighter. The wing for the new aircraft was configured to accommodate twelve 7.7mm Colt Browning guns; a 50 per cent increase on the firepower of the Hurricane. The 'private venture' design initiative on the part of Hawkers was independent of any Air Ministry plans for future fighters. The Air Ministry, at the time Hawkers were designing the twelve-gun fighter, issued Specification F 18/37 for a four-20mm gun single-engine, fighter to complement the twin-engine Specification F 37/35 of 1935 that led to the four 20mm-gun Westland Whirlwind. Eventually Sydney Camm, Chief Designer of Hawkers. was persuaded to postpone further design work on the twelve-gun fighter and wait for F 18/37 to be officially distributed to the ten on the Ministry's list of favoured companies. The specification, including the operational requirements, arrived at Kingston in January 1938. Apart from the four 20mm-gun requirement Camm's 12-gun proposal came very close to the requirement of F 18/37"

Source: The Lion has Wings by L F E Coombs

Yes, there were difficulties with early Spitfire production - it was a 'new' aircraft British Aircraft industry hadn't advanced - hence Hawkers found it easier to build the old style Hurricane, and for the Spitfire there was the 'Nuffield' factor, Castle Bromwich in Vickers hands earlier would solve that.
IMHO if there had been no Spitfire, then the Air Ministry would have wanted something else - that could have been available in the same time frame. It probably wouldn't have been as good as a Spitfire, yet likely to have been better than the Hurricane! Indeed, with no Spitfire in the pipeline earlier, Boulton-Paul may have won big - the P.88 gets built 'a' not 'b' gets ordered - which could be developed - Tornado/Typhon still born, and a single-seat Defiant is possible.

 

[wuzak]

Another thing, the Merlin 60 series was designed for high altitude bombers. It was Hives who suggested that it be put in the Spitfire. I wonder if he would have been so enthused about sticking it in the Hurricane?

 

[Shortround6]

Climb rates aren't that different either as the Hurricane has more lift due to the lower wing loading but this is hard to compare because of the often different armament and armour loadings.

Climb is NOT dependent on lift. It is dependent on excess power at at what ever speed is being compared.
If both planes are doing 160mph and plane B needs 80hp less than plane A to do 160mph due to drag and both have the same engine than plane B has 80 more HP for climb. It now becomes a power to weight thing, not lift.
If both planes are doing 330mph and plane A can only do 330mph but plane B can do 360mph then plane B can climb (slowly) while doing 330mph. It has excess power available.

The Spitfire has the edge in dive but a cleaned up Hurricane would improve on the historical Hurricane.

Possibly, possibly not. Dive limits also include limiting the dive speed due to handling problems AND structural limitations.

I'm not arguing that the Hurricane is a better fighter, but more capable Hurricanes, sooner would have improved the Commonwealth's strategic position in 1941.

The Commonwealth also needed better trained pilots and better tactics. A plane half way between a MK I and MK II Hurricane isn't going to do much.

The 16lbs of boost doesn't seem to have been available until near the end of 1942. Merlin XX and 45 were introduced at 9lbs. Merlin IIIs and later Merlins in 1940-41 may have used 12lbs but it was COMBAT only. NOT for routine take-offs or climbs to altitude.

Hurricanes got Merlin XX engines because WITHOUT it they were considered toast. It was a way to keep the Hurricane competitive in late 1940, early 1941 to keep up the numbers of fighters, much like you are saying but the Hurricanes performance was already considered distinctly second rate. Combat was occurring at 25,000ft and above (or it was starting at 25,000ft and above) and at 25,000ft a Spitfire I could climb 31% faster than a Hurricane MK I and at 30,000ft the difference was 54%.
Maybe these figures are not 100% accurate but it was from tests done at the time and helped shaped the policy.

With the Merlin XX the Hurricane, while still slower, could out climb the Spitfire and more importantly the 109E-3. With less capable engines than the XX the Hurricane would have been in serious trouble vs the 109F in 1941. It was in serious trouble even with the XX.

The Spitfire had to make do with the single speed engines because there weren't enough XXs to go around, Bomber command was hogging a bunch because the Hercules was little late in showing up.

 

[nuuumannn]

I wonder if he would have been so enthused about sticking it in the Hurricane?

Well, they did agree to fit a Griffon to a Hurricane at one stage. I suspect though, that Merlin 61 production (for fighters as opposed to the Merlin 60 in the Wellington VI) was allocated to Spitfire production even before N3297 took to the air in September 1941. This certainly became the case once the Fw 190 appeared and the Air Minsitry suggested the stop gap Mk.V fitted with a Merlin 61, although 500 engines at Hucknall were allocated for Mustang I use, oddly enough.

 

[Aozora]

Where you got those figures from I have no idea, they are clearly inaccurate:

The problem with this, is that there werent 27 to shoot down. Thats a bit of a problem with that account. There were a total of 50 Hurricanes delivered June 1940 through to the end of May 1941. 8 were delivered in June 1940, but these had been gradually lost or grounded as i understand it by action with the italians, before the entry of the Germans on the scene. There was a reinforcement of 12 Hurricanes provided in November, 12 flown off, but only 4 made it. There was another resupply before March, such that the available strength March and April was about 23 aircraft. Another 5 were lost in delivery. There was a major resupply by Ark Royal towards the end of April, andother one lost enroute. Hurricanes were lost on the ground or to noncombat related causes in March (that might be a doubleing up from the 5 lost and mentioned previously.

Putting that all together, 8 lost before the arrival of the Germans, 15 lost at sea, or on the ground, 16 (or 19) still serviceable at the beginning of June '41. That adds up to 39 not shot down by the German 109s. Sorry if that does not correlate to Shores, or anyone else, but they are semi official figures 9cant be official since many of the early war strength returns for the Malta defence command were destroyed in air raids. That means that my sources are aas good as yours.

Areas where I may be wrong....perhaps the italians did not shoot down all 8 of the June defenders, in which case you might assume up to 8 more. but most accounts admit to the loss of 8 Hurricanes to the end of December 1940. If those losses were in fact by Germans, then your victories for the 109s could be bumped up to 19. But the overall loss rates for the Huricanes remains fixed, iut just means more credit needs to be given to the 109s. Doesnt alter the overall losses suffereed by the Axis, doesnt alter the overall losses suffered by the hurricanes, and doesnt disprove that the claim the hurricanes were "slaughtered" is a total post war myth. I'll take 20-50 Hurricanes lost in exchange for 230 Axis aircraft any day and claim it a victory every time, especially when the defenders are outnumbered 17:1. .

As I very clearly pointed out Shores, Cull and Malizia have done a thorough job of listing the Hurricane's serial numbers and, where possible, their pilots in a day to day breakdown: as it is

Areas where I may be wrong....perhaps the italians did not shoot down all 8 of the June defenders, in which case you might assume up to 8 more. but most accounts admit to the loss of 8 Hurricanes to the end of December 1940. If those losses were in fact by Germans, then your victories for the 109s could be bumped up to 19.

is totally irrelevant because I am not discussing losses from 1940 - I am describing the period when 7./JG26 was operating over Malta and shot down 27 Hurricanes for no loss.

If you don't want to believe that 27 Hurricanes were shot down by 109s during that period that's your pigeon, but I would advise you read the book and evaluate its accuracy before dismissing it as nonsense.

97 Hurricanes delivered November to May, all of which stayed on Malta.

 

[Aozora]

Hurricane development was stopped because the Spitfire existed.

As has been pointed out, Hurricane development was slowed (not stopped entirely) because Camm and the design team had moved on to designing and developing the Typhoon/Tornado, which promised far more scope in performance and development potential.

If it didn't exist, and the time and money that went into the Spitfire was used to build more Hurricanes, then there would also be more incentive to develop the Hurricane further.

BUT the Air Ministry did not think about devoting more time, resources or money to the Hurricane over and above that which had already been allocated; as I have already pointed out, when a plan was mooted to halt Spitfire production the favoured alternatives were the Beaufighter or Whirlwind - the Hurricane was not considered, except in passing.

This doesn't mean that other designs wouldn't be considered and developed, but with so many Hurricanes being built, even small increases in performance would have been worthwhile.

This assumes that magically more Hurricanes would have been built, which, as has been explained several times, was not seriously considered pre-war. Other designs would most definitely have been developed once it was realised that the Hurricane was semi-obsolescent in 1940.

 

[drgondog]

Strictly speaking Rate of Climb = Excess Power/Weight
1.) ROC =(Thrust*Velocity-Drag*Velocity)/Weight.

To get to 1.)
2.) Rate of Climb is V*Sin(theta) where theta = angle of climb and V=Freestream velocity of flight path in climb

Developing a Free Body force diagram along the flight path axis and perpendicular to the axis

3.) Parallel forces T=D+W*sin(theta), Perpendicular forces L=W*cos(theta) as both L and D are expressed along the flight path

4.) Solving for the Vertical component of Velocity to achieve (ROC),
T*V=D*V+W*V*sin(theta)

5.) Re-arranging for ROC=V*sin(theta)= (T*V-D*V)/W

Now - Drag from above = Zero Lift Drag plus Induced Drag = CDo+(CL>>2)/(pi*AR*e)

But CL = L/(1/2*rho*(V>>2)*S) = function (k*L/S)

So, strictly speaking Drag, and therfore ROC, Is affected by Wing Loading.

 

[nuuumannn]

So, strictly speaking Drag, and therfore ROC Is affected by Wing Loading.

I coulda told you that without all that extra stuff...

 

[parsifal]

As I very clearly pointed out Shores, Cull and Malizia have done a thorough job of listing the Hurricane's serial numbers and, where possible, their pilots in a day to day breakdown

So do the two authors I quoted. no-one is above questionng, and there is no definitive answer to this problem, because the records many of the records kept for this period were destroyed. Thats what makes the problem difficult to unravel

is totally irrelevant because I am not discussing losses from 1940 - I am describing the period when 7./JG26 was operating over Malta and shot down 27 Hurricanes for no loss.

No, it isnt. Its possible that those aircraft that were delivered in June (and August (I knew about that delivery but forgot....they too were gone by January) were still around in January '41. Its unlikley, and the conventional accounts do say they were lost before then

If you don't want to believe that 27 Hurricanes were shot down by 109s during that period that's your pigeon, but I would advise you read the book and evaluate its accuracy before dismissing it as nonsense

.


Who said anything about nonsesne, except yourself. I should say the same for you, you should read the accounts ivereferenced before dismissing them

97 Hurricanes delivered November to May, all of which stayed on Malta.

What you posted doesnt actually say that. It says 333 Hurricanes were delivered August 1940 to November. It then says that of the 333 that arrived safely at Malta, 150 staged to North Africa. It doesnt say when. I knew about them as well. Given that no new Hurricane squadrons were formed on theisland until the very end of the campaign (after the arrival of 40 odd in late May) it is highly likley that some of the aircraft arriving in the first half of 1941 also staged to NA as well. My guy does talk about that as well.

In any event, even if you want to argue the toss and say that 27 were shot down, at the end of 1941, the strength returns for the now 4 squadrons on the island were about 50 a/c. By that stage they had shot down 181 Italian and 81 German aircraft, in exchange for the loss of 120 or so of their own number (based on your figures). There were a few other fighters as well, mostly Fulmars, but it was the hurricanes doing the heavy lifting, and for an admitted obsolete aircraft, that aint half bad, and a long way from being "slaughtered" The fact that they were going for the bombers, and not the Axis fighters makes all the sense in the world. The loss rates if you want to press your own numbers, or mine (it doesnt matter really, because thats not the point of the discussion) underline the fact that advantages in fighter technology have virtually no effect on overall loss rates. They do in terms of fighter on fighter, but thats just a glorified p*ssing contest....the real game is whether your bombers are being shot down or not. And axis bombers were being shot down..... Numbers and training do.....Its important and worth noting that more than half the 42 claimed victories by JG 26 were done by 2 or 3 men.

And 120 in exchange for 260 is not a slaughter, at least for the allies. Moreover, Malta continued to act as an effective base (albeit at the end less so).

 

[RCAFson]

The Commonwealth also needed better trained pilots and better tactics. A plane half way between a MK I and MK II Hurricane isn't going to do much.

LoL, you keep trying to pretend that the Merlin 12/45 has no advantage over the III when demonstrably, this is not true. The Merlin 45 would have given the Hurricane 1 a substantial edge in performance over the III.

The 16lbs of boost doesn't seem to have been available until near the end of 1942. Merlin XX and 45 were introduced at 9lbs. Merlin IIIs and later Merlins in 1940-41 may have used 12lbs but it was COMBAT only. NOT for routine take-offs or climbs to altitude.

According to Lovesey Merlin 45/16lb boost was available in Dec 1941 and I know it was used in mid 1942 because it is mentioned in an August 1942 report on how to counter the FW-190

Hurricanes got Merlin XX engines because WITHOUT it they were considered toast. It was a way to keep the Hurricane competitive in late 1940, early 1941 to keep up the numbers of fighters, much like you are saying but the Hurricanes performance was already considered distinctly second rate. Combat was occurring at 25,000ft and above (or it was starting at 25,000ft and above) and at 25,000ft a Spitfire I could climb 31% faster than a Hurricane MK I and at 30,000ft the difference was 54%.
Maybe these figures are not 100% accurate but it was from tests done at the time and helped shaped the policy.

You are comparing the climb rates of an overloaded Hurricane 1 with a standard loaded Spitfire 1. Using normal loading for both gives Hurricane/Spitfire I times to 20,000 and 30,000 ft of 8.35/7.7 and 18.3/16.4 minutes with climb rates at each altitude of 1675/1840 and 530/660fpm so the difference is about 10% and 20%.

With the Merlin XX the Hurricane, while still slower, could out climb the Spitfire and more importantly the 109E-3. With less capable engines than the XX the Hurricane would have been in serious trouble vs the 109F in 1941. It was in serious trouble even with the XX.

A Hurricane with a Merlin 12 or 45 is still going to have a substantial edge over the same Hurricane with a Merlin III - I don't know why this is so hard for you to acknowledge.

The Spitfire had to make do with the single speed engines because there weren't enough XXs to go around, Bomber command was hogging a bunch because the Hercules was little late in showing up.

After the 45/46 was cleared for 16lb boost, it had a very clear advantage on the XX, and even before then there were advantages in weight reduction and engine management/reliability with the 45.

 

[RCAFson]

If there was no Spitfire, another manufacturer - possibly Boulton Paul with what became the P.94 single seat Defiant, would have produced a second fighter, as both Aozora and Wuzak have mentioned before. As for Hawker, things would not have gone any differently than the way it did in real life; effort would have been concentrated on the Typhoon and Tornado, not further developing the Hurricane. Here is a passage from British Secret projects Fighters and Bombers 1935 - 1950 by Tony Buttler;

The whole premise for this thread is that the UK decides not to build the Spitfire but to instead use the funds and factory space to build more Hurricanes. You might call it a quantity over quality approach, or "good enough" in large numbers is better than "best" delivered too late. For example, there was a total of 16 hurricanes delivered to Malta via aircraft carrier in 1940, and none existed there in June 1940. With abundant numbers, sooner, the RAF/FAA can have Hurricanes in the MTO in substantial numbers prior to the Italian entry into the war giving the RN much better fighter cover and ensuring that Malta, in return receives enough Hurricanes to achieve air superiority from the start.

 

[RCAFson]

I agree, Cobber. RCAFson, you are presuming that what would have happened between when the Hurricane prototype first flew and WW2 things would have been different had there been no Spitfire and this is based on what you know about WW2. Your entire argument is based on hindsight, which they did not possess when the Hurricane was being built. You have to remember that when the Hurricane first entered service it was considered the pinnacle in fighter development - the British did not know, nor could they have predicted that Willi Messerschmitt's fighter was going to be better than the Hurri Mk.I in the form of the Bf 109E, so why would the Air Staff, or Hawker insist that the Hurricane undergo drastic improvement before the war, especially since the firm was developing a replacement?

The Air Staff had such faith in the aircraft's design that the biggest British peacetime order for aircraft up to that time was placed with Hawker to build Hurricanes - 600 of them. The Langley production line was built specifically to meet the need - and because Hawker's existing facilities were little more modern than what they had been under Sopwith use in WW1 and Gloster got an order as well - this was instead of Wellingtons, that C-in-C Bomber Command Cyril Newall had hoped for. Deficiencies in its performance against the Bf 109 only became evident in the spring/summer of 1940, by then, better fighters had already flown and were being built, as mentioned earlier. Nothing would have been any different within Hawker before the outbreak of war, even if there wasn't a Spitfire.

The relative performance of the 109 and Hurricane is irrelevant. The UK government and AM were being constantly warned that Nazi Germany was building up a massive AF much more rapidly than the RAF, and early UK intelligence reports seemed to confirm this. Even without hindsight, it was therefore, easy to make a case for a much more rapid expansion of RAF FC, and the most logical fighter to be mass produced was the easy to build, easy to repair, and easy to fly, Hurricane.

 

[RCAFson]

Where you got those figures from I have no idea, they are clearly inaccurate:

From Malta: The Hurricane Years 1940-41 (a day to day chronicle):

Between February 1941 and late May Hurricanes shot down in air-to-air combat by 7./JG26 = 27 with no losses to 7 Staffel. (pages 146 - 225) In one-on one fighter combat that is a slaughter.

Yes and reading the above book leaves one in no doubt that the Hurricanes were greatly outnumbered, not only by 110/109s but also by the numerous IAF fighters operating from Sicily. In any event, the 109s were able to achieve 5.4 kills per month by using hit and run tactics while the Hurricanes were engaged with the bombers and/or the IAF fighters - hardly a stellar achievement when total production was about 2500 over those 5 months. Typical numbers of serviceable Hurricanes were on the order of 15/day versus axis raids escorted by ~3 times that many fighters. Additionally many of the Hurricanes were Mk 1 trops, since they were originally intended for the WDAF.

 

[Shortround6]

LoL, you keep trying to pretend that the Merlin 12/45 has no advantage over the III when demonstrably, this is not true. The Merlin 45 would have given the Hurricane 1 a substantial edge in performance over the III.

Oh, it has an advantage over the Merlin III, just not as much as you think.

You are comparing the climb rates of an overloaded Hurricane 1 with a standard loaded Spitfire 1. Using normal loading for both gives Hurricane/Spitfire I times to 20,000 and 30,000 ft of 8.35/7.7 and 18.3/16.4 minutes with climb rates at each altitude of 1675/1840 and 530/660fpm so the difference is about 10% and 20%.

Thank you

A Hurricane with a Merlin 12 or 45 is still going to have a substantial edge over the same Hurricane with a Merlin III - I don't know why this is so hard for you to acknowledge.

I can acknowledge it, what you seem to be missing is that the Merlin 45 doesn't show up for 4-6 months AFTER the XX meaning these Hurricanes that are "superior" to the MK I but inferior to the MK II aren't going to show up for squadron use until the spring of 1941. Why build a Hurricane 1.5 when the II has been in production for 6 months? Especially when the II won't do the job?

After the 45/46 was cleared for 16lb boost, it had a very clear advantage on the XX, and even before then there were advantages in weight reduction and engine management/reliability with the 45.

OK, why would it have an advantage over the XX? and at what altitude?
as for the rest you are grasping at straws, weight reduction??? 65-75lb in an over 6000lb airplane? Engine management? Reliability? how much trouble was the two speed drive??

How much is the loss of about 100hp at take-off and at altitudes below 6,000ft or so worth? how much is the lower critical height of the Merlin 45 worth?

 

[RCAFson]

I can acknowledge it, what you seem to be missing is that the Merlin 45 doesn't show up for 4-6 months AFTER the XX meaning these Hurricanes that are "superior" to the MK I but inferior to the MK II aren't going to show up for squadron use until the spring of 1941. Why build a Hurricane 1.5 when the II has been in production for 6 months? Especially when the II won't do the job?

Actually, that's not true at all. The Merlin 12/SpitfireIIA began to arrive in quantity in June/July 1940 and by Aug 1940 two squadrons had moved over entirely to the 2A and by the end of the BofB 7 squadrons had the IIa. What isn't commonly known is that earlier introduction of the IIA was thwarted, not by problems at RR, but by the poor output of the Nufield Spitfire factory, so in all probability, the Hurricane/Merlin 12 could have appeared in much larger numbers than the Spitfire IIa, much sooner. Early Nufield production was limited because the Spitfire took longer to mature and required more engineering and design changes, which frustrated Nufield's ability to get into full production. The more mature Hurricane design would have allowed for full output months sooner, and more output per man-hour.

OK, why would it have an advantage over the XX? and at what altitude?
as for the rest you are grasping at straws, weight reduction??? 65-75lb in an over 6000lb airplane? Engine management? Reliability? how much trouble was the two speed drive??

How much is the loss of about 100hp at take-off and at altitudes below 6,000ft or so worth? how much is the lower critical height of the Merlin 45 worth?

The early XX has to be throttled back at the gear change points (just look at the performance curves), or you risk losing the engine. The 45 can simply be run flat out right from TO. I've already pointed out that the XX installation was actually ~200lbs heavier (at least part of this is due to the increased length of the installation).

Harvey-Bailey specifically mentions that the 2spd installation was troublesome, and both gear and clutch failures occured in the early production engines. I would suspect that they weren't fully cured until the Merlin 24 appeared.

In any event the XX is still going to be on the scene, but now it will be supplement by improved single stage engines as well.

 

[Shortround6]

Actually, that's not true at all. The Merlin 12/SpitfireIIA began to arrive in quantity in June/July 1940 and by Aug 1940 two squadrons had moved over entirely to the 2A and by the end of the BofB 7 squadrons had the IIa. What isn't commonly known is that earlier introduction of the IIA was thwarted, not by problems at RR, but by the poor output of the Nufield Spitfire factory, so in all probability, the Hurricane/Merlin 12 could have appeared in much larger numbers than the Spitfire IIa, much sooner.

The Merlin 12 is NOT an early Merlin 45. It is a Merlin III using water/glycol instead of pure glycol as coolant and using a slightly higher supercharger gear on the Merlin III supercharger.

The early XX has to be throttled back at the gear change points (just look at the performance curves), or you risk losing the engine. The 45 can simply be run flat out right from TO. I've already pointed out that the XX installation was actually ~200lbs heavier (at least part of this is due to the increased length of the installation).

First part is true but then every other two speed engine in the world had to be throttled back to change gears too, didn't they? The 45 CANNOT be run flat out from take-off. It can be run at 2850rpm at 9lb boost after take-off which is the same as the Merlin 12 or the Merlin XX.
How much of the 200lb installed weight is the engine, how much is the "extra length" and how much is the change in the cooling system from pure glycol to the water/glycol mix and any changes in the radiators? How much of the extra length is the two speed drive and how much is the extra length of the new intake elbow on the Hooker designed supercharger used on both the XX and the 45?

Lets make sure we are comparing apples to apples. Some planes fitted with the Merlin XX (like the Defiant) had to have bigger radiators installed to handle the extra power and that is before they pushed the boost up to 16lbs. Didn't Spitfires with Merlin 45s get bigger oil coolers than Spitfires with Merlin IIIs ?

Lovesey specifically mentions that the 2spd installation was troublesome, and both gear and clutch failures occured in the early production engines. I would suspect that they weren't fully cured until the Merlin 24 appeared.

In any event the XX is still going to be on the scene, but now it will be supplement by improved single stage engines as well.[/QUOTE]