# P-38 with Merlin Engines? Any such animal?



## Messy1 (Jun 24, 2008)

I was watching Showdown on the Military Channel this past weekend. The episode was the P-38 vs. Zero. A question came to mind. Did anyone ever experiment with replacing the Allison engines in the P-38 with RR Merlins? Was this ever done? Was or would there be any benefit? Just curious to see what the many fine minds on here thought or know about this?


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## HoHun (Jun 24, 2008)

Hi Messy,

>Did anyone ever experiment with replacing the Allison engines in the P-38 with RR Merlins? Was this ever done? Was or would there be any benefit? 

I believe there were some thoughts historically about such a conversion, but as far as I know no conversion ever resulted.

I once prepared a rough calculation of the effect of using mechanically supercharged Merlins instead of turbo-supercharged Allisons, and while the results vary with the exact subtypes of each engine model one might consider for installation, my conclusion was that the Allisons as installed in the P-38 were an excellent choice for the aircraft, and that the Merlins probably would not have improved general performance even if they could have fit into the same airframe with the same aerodynamic efficiency as the original Allisons.

This conclusion somewhat suprised me, as the Merlin for example enjoys the benefit of a substantial increase in effective power over the rated values from the thrust of its exhausts which the turbo-supercharged Allisons lack, but the greater full throttle height of the Allisons helped to make up for the diference, and possibly more.

This is nothing final of course, just my best guess at the time when I did said analysis a couple of years back.

Regards,

Henning (HoHun)

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## SoD Stitch (Jun 24, 2008)

Not long after the P-38 entered service, Hal Hibbard and Clarence "Kelly" Johnson did propose installing Packard-built Merlins in the Lightning, which would've made the P-38 a world-beater; but the Army Materiel Command told Lockheed that all of the Packard-built Merlins were already slated to go to Mustangs. I have a book which discusses this episode in some detail, I'll see if I can track it down. The author of the book is fairly convinced that there were unknown forces working behind the scenes to deny installing superior engines in the P-38; sounds a little like a conspiracy theory to me, but you gotta wonder why it never happened. With improved high-altitude performance, the up-engined P-38 might've negated the need for the P-51D in the ETO, at least temporarily.


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## FLYBOYJ (Jun 24, 2008)

The Merlin P-38 never happened because there were no guarantee it was really going to improve anything (look at the Merlin powered P-40s) and the engines were GFE - government furnished. It was at the government's request that the Allison was chosen and remained the powerplant of the P-38.

Besides introducing a mod like that was no easy task - the P-51 was way more adaptable to the Merlin than the P-38 - it's not a matter of "just bolting it on." Not only does the nacelle have to be re-designed but the whole QEC had to be re-engineered for ease of assembly and maintenance.

With or without the Merlin, the P-38L was the ultimate P-38 model.


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## SoD Stitch (Jun 24, 2008)

FLYBOYJ said:


> Besides introducing a mod like that was no easy task - the P-51 was way more adaptable to the Merlin than the P-38 - it's not a matter of "just bolting it on." Not only does the nacelle have to be re-designed but the whole QEC had to be re-engineered for ease of assembly and maintenance.



If I had to guess (and I do!), I would say the two-stage supercharger bolted to the rear of the Merlin would've caused major problems installing it on the P-38; the turbo-supercharger for the Allisons was _behind_ the main landing gear on the P-38, in the boom. I think the supercharger on the Merlin would've intruded into the main wheel wells on the P-38, necessitating a complete redesign of the nacelles.


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## FLYBOYJ (Jun 24, 2008)

Yep.....


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## Messy1 (Jun 25, 2008)

Good Info! I was wondering about the engine fit myself. It would have been interesting to see a comparison between an Allison and a Merlin powered P-38.


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## KrazyKraut (Jun 25, 2008)

The P-38 did pretty well with the Allison. In fact it was probably the best plane with that engine. People have to realize that engines aren't available at will. The avialable Merlins were probably put to better use in the P-51 especially with the mentioned modifications needed to the P-38 airframe. You can also speculate how good the Hs-129 could've been with a BMW 801, but these engines were needed elsewhere.


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## Marshall_Stack (Jun 30, 2008)

I read in Warren Bodie's book that there may have been some politics involved with using Allison's over the Merlins. Something to do with an Army officer close to the project used to be an exec with GM (who owned Allison) and probably still had stock in GM.

Warren is pretty much of the opinion that the Merlin would have been a good idea. The turbocharging system was having a problem at high altitude in Northern Europe.


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## FLYBOYJ (Jun 30, 2008)

Although I have a lot of respect for Bodie, I think that's just a myth. Again, the redesign for the installation of merlins would have been immense with no guarantee of substantiated performance.

Again, amazing that the same problems weren't that wide spread in the Pacific.

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## SoD Stitch (Jun 30, 2008)

Marshall_Stack said:


> I read in Warren Bodie's book that there may have been some politics involved with using Allison's over the Merlins. Something to do with an Army officer close to the project used to be an exec with GM (who owned Allison) and probably still had stock in GM.
> 
> Warren is pretty much of the opinion that the Merlin would have been a good idea. The turbocharging system was having a problem at high altitude in Northern Europe.



Yes, that's the same book I have; here's what Brodie has to say about the "Army officer close to the project":

"No real proof exists, but it must be a fact of life that Lt. Gen. Knudson was not going to do anything that would hurt General Motors (wartime manufacturer of the Allison engine). After all, he had been a top executive with that corporation for years until he had accepted his appointment to the Office of Production Management at the beginning of the new decade. It would be ludicrous to believe that he would throw more plums to competitor Packard (builder of the Merlins) at the expense of G.M., and it is also likely Knudsen held a large block of stock in the corporation. (In those days, it was not necessary to give up your stock holdings when a "conflict of interest" might occur)."


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## drgondog (Jun 30, 2008)

FLYBOYJ said:


> Although I have a lot of respect for Bodie, I think that's just a myth. Again, the redesign for the installation of merlins would have been immense with no guarantee of substantiated performance.
> 
> Again, amazing that the same problems weren't that wide spread in the Pacific.



Two reasons come to mind Joe. Both related

1. The fights in the PTO were so rarely above 15-20K and most were below that altitude - far more like MTO in summer.
2. The relative temps for altitude were higher in PTO versus ETO.


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## syscom3 (Jun 30, 2008)

And the 11th AF in the Aleutions didn't have the same problems the 8th AF did.


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## FLYBOYJ (Jun 30, 2008)

drgondog said:


> Two reasons come to mind Joe. Both related
> 
> 1. The fights in the PTO were so rarely above 15-20K and most were below that altitude - far more like MTO in summer.
> 2. The relative temps for altitude were higher in PTO versus ETO.


Point taken and agree, but as we know corrected on the later models...


syscom3 said:


> And the 11th AF in the Aleutions didn't have the same problems the 8th AF did.


Yep!!!


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## Marshall_Stack (Jul 1, 2008)

syscom3 said:


> And the 11th AF in the Aleutions didn't have the same problems the 8th AF did.



As for that argument (and I am just relaying the info, not claiming to be an expert), I read that the P-38's in the Alaska weren't flying as high (since they were escorting low-flying bombers) and that the temps still weren't as cold as Northern Europe. 

I have also read that they operated differently; in one theatre they had high RPMs but low manifold pressure and vice versa. Again I'm not a pilot or expert but that was claimed as a possible difference in performance. I'm interested in comments to this claim.....


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## FLYBOYJ (Jul 1, 2008)

Marshall_Stack said:


> As for that argument (and I am just relaying the info, not claiming to be an expert), I read that the P-38's in the Alaska weren't flying as high (since they were escorting low-flying bombers) and that the temps still weren't as cold as Northern Europe.


Possibly, but Northern Europe vs Alaska in temperature?


Marshall_Stack said:


> I have also read that they operated differently; in one theatre they had high RPMs but low manifold pressure and vice versa. Again I'm not a pilot or expert but that was claimed as a possible difference in performance. I'm interested in comments to this claim.....


Higher Manifold pressure and lower RPM - I think Lindberg taught that as well.

I would bet the Alaskan P-38 drivers were a lot more proficent in twin engine aircraft operations as well.


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## Marshall_Stack (Jul 1, 2008)

This website has some interesting info relating to the problems of P-38s in the ETO (for those who have not yet read this....)

P-38: Der Gabelschwanz Teufel


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## FLYBOYJ (Jul 1, 2008)

Good site, the title is a myth....


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## uberdave (Jul 15, 2008)

I always wondered why the US didn't standardize on the Merlin for inline engines. I remember seeing a book (don't remember the title) about P38s which had a photo of what it claimed was a P38 w/ Merlins. I don't remember what else the book had to say about the experiment.


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## FLYBOYJ (Jul 15, 2008)

uberdave said:


> I always wondered why the US didn't standardize on the Merlin for inline engines.


Because they weren't always the "perfect" solution for aircraft - some P-40 models had them and performed worse... 


uberdave said:


> I remember seeing a book (don't remember the title) about P38s which had a photo of what it claimed was a P38 w/ Merlins. I don't remember what else the book had to say about the experiment.


A P-38 was never fitted with Merlins - period!


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## Broncazonk (Jul 15, 2008)

The P-38K

*The Story Of The Best Performing Variant Of The P-38 Lightning - P-38K*

The Lockheed P-38K-1-LO is now nearly forgotten. No photographs of the aircraft are known to exist today. Only the original test mule was photographed. It has been relegated to that part of history where one off prototypes and special test aircraft usually go. This is rather unfortunate for this aircraft as it was the benchmark against which all other variants of the P-38 Lightning must be compared. Simply said, it was the best performing Lightning ever to take to the sky.

From the very beginning of America’s involvement in World War Two, Lockheed was looking for ways to improve the performance of the P-38. The installation of Rolls Royce XX Merlins was seriously considered. Lockheed went as far as designing the installation package. The advantages of the Merlin engine were numerous. First and foremost was the elimination of the complex turbocharger system. This would also result in a much cleaner engine nacelle. The turbo intercoolers could be removed. That would have allowed for a for more aerodynamic package, closer in shape to that of the original XP-38. Another option was to remove the Prestone radiators and place them under the engine as in the P-40. This location had the additional advantage of reducing the length of the cooling system plumbing. This, in turn, reduced the risk of battle damage to the system. Either option would result in a significant reduction in drag and weight. A further benefit would be gained by the removal of intercooler ducting in the front portion of the outer wings. This volume could be utilized for increased fuel capacity. In fact, that is what was done when the P-38J was designed with revised intercooler cores that eliminated the ducting. This increased internal fuel capacity by 110 gallons.

There were some performance areas that would suffer. While a gain in speed at medium altitudes was expected, the rate of climb would be reduced by as much as 400 feet per minute. Service ceiling would also be reduced as the Packard Merlin XX made considerably less power above 30,000 feet than did the Allison V1710. At the time, no one anticipated the engine and turbocharger problems that developed at high altitude over Europe. Unfortunately, the War Production Board was unwilling to shut down the production line for several months to retool for major design changes required for the engine swap. As a result, the Merlin project was shelved. No P-38 ever flew fitted with Rolls Royce Merlin or Packard engines. The idea of retro-fitting Merlin 61 engines was bantered about 8th Air Force Fighter Command, however there is no evidence that any such conversion ever took place. The prospect of such a modification would have been daunting. This was no simple engine swap, it required large portions of the airframe to be completely redesigned. Stories of Merlin powered Lightnings are, without much doubt, myth. 

This, however, did not put an end to seeking greater performance. Lockheed paid close attention to the performance gains achieved with the P-47 when the new "high activity" Hamilton Standard propellers where first fitted on a Republic P-47C in mid 1942 (later, in mid 1943, these propellers were retro-fitted in Britain). The new "paddle" blade prop had significantly increased the rate of climb and acceleration of the "Jug". Lockheed decided that they would install the Hamilton Standard hydraulic propellers on one of the factory test "mules". Thus, was the XP-38K born. The "mule" was an extensively modified P-38E. The original intercoolers were replaced with the newer type introduced on the J model. The initial test results were very encouraging and a P-38G service test airframe (422-81, AFF serial number 42-13558) was selected to be modified.

The new propellers were not the only design changes made in the search for greater performance. This airframe was configured for the Allison V1710F-15 powerplants which were rated at over 1,875 bhp in War Emergency Power (as compared to 1,725 bhp for the V1710F-17 in the P-38L). This was the only P-38 so configured. The potent combination of the engine/propeller promised excellent performance. 

There were still other modifications that were necessary. The Hamilton Standard props required a spinner of greater diameter, and the thrust line was slightly higher as well. This in turn, required that new cowlings be manufactured to properly blend the spinners into the engine nacelles. These were hand made and the fit was less than perfect. The new propellers necessitated a change to the reduction gear ratio. The Curtiss Electric props had a normal ratio of 2.00 to 1. The ratio was changed to 2.36 to 1.

Flight tests were conducted from late February through the end of April 1943. Performance was better than hoped for. Maximum speed at critical altitude (29,600 ft) was 432 mph (Military Power). At 40,000 feet, the "K" zipped along at a speed that was 40 mph faster than the current production P-38J could attain at this same height. Maximum speed in War Emergency Power, at critical altitude, was expected to exceed 450 mph. The increase in ceiling was just as remarkable. Flown to 45,000 ft on an extremely hot and humid day, Lockheed engineers predicted a "standard day" service ceiling in excess of 48,000 ft! Improvement of the cowling fit and the elimination of the heavy coat of paint would have gained even more performance. Due to the added efficiency of the new propellers, range was expected to increase by 10 to 15 %. Lockheed appeared to have a world-beater on their hands.

The plane, now designated the P-38K-1-LO was flown to Elgin Field for evaluation by the USAAF. Flown against the P-51B and the P-47D, this Lightning proved to be vastly superior to both in every category of measured performance. What astounded the evaluation team was the incredible rate of climb demonstrated by the P-38K. From a standing start on the runway, the aircraft could take off and climb to 20,000 feet in 5 minutes flat! The "K", fully loaded, had an initial rate of climb of 4,800 fpm in Military Power. In War Emergency Power, over 5,000 fpm was predicted.

In light of this incredible level of performance, you would certainly expect that the Government would be falling all over themselves to quickly get the P-38K into production. Yet, this was not the case. The War Production Board was unwilling to allow a short production suspension in order to get new tooling on line for the required change to the engine cowling. Even when Lockheed promised that the stoppage would only be for 2 or 3 weeks, their request was turned down.

The true consequences of this pig-headed thinking will never be known. What would have been the impact of such a high performance fighter arriving in force to the forward combat areas in mid 1943? How many lost fighter pilots would have survived thanks to the awe inspiring performance of the P-38K? Again, we can never know these things. What we do know, is that due to bureaucratic myopia, neither the P-38K nor a Merlin powered Lightning ever really had a chance to make an impact upon the air war. For all those pilots who died at the controls of lesser aircraft, the War Production Board bears a measure of responsibility for their fate.


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## Broncazonk (Jul 15, 2008)

The above was from: The P-38K

I think the original material appeared in the P-38 book by Warren M. Bodie.


Bronc


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## FLYBOYJ (Jul 16, 2008)

> Stories of Merlin powered Lightnings are, without much doubt, myth.



There you have it....


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## Messy1 (Jul 16, 2008)

Pretty much closes the book on that I think.


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## HoHun (Jul 16, 2008)

Hi again,

>I once prepared a rough calculation of the effect of using mechanically supercharged Merlins instead of turbo-supercharged Allisons

Well, here is a new calculation along the same lines ... just a quick estimate, nothing final, but it illustrates the differences between the two types of engines.

Regards,

Henning (HoHun)


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## FLYBOYJ (Jul 16, 2008)

Interesting stuff Henning - based on the calculations I guess a Merlin P-38 really wasn't worth the effort!


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## Messy1 (Jul 17, 2008)

Well thanks everyone for answering my question.


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## Oreo (Jul 19, 2008)

When you look at all the aircraft of the war that were extensively modified to take different engines-- sometimes with great success, sometimes with dismal failure, or no gain at all, and the reckless abandon with which A/C designers of all the major nations did this, it seems to me quite astounding that the P-38 never got fitted for the Merlin, ditto the P-39. I'd also like to point out another high-performer with the Allison was the P-63, which the Russians loved. And for those of you poo-pooing the use of the Merlin on the P-40-- it is true the speed did non increase much, but the climb rate was up drastically, and so was the service ceiling. And what would keep them from having used a turbocharger system like the P-38 had, for the Merlin engines, rather than the supercharger system? The turbo system was more effective (I guess) in terms of ceiling and high altitude performance.


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## red admiral (Jul 19, 2008)

> The turbo system was more effective (I guess) in terms of ceiling and high altitude performance.



Rolls-Royce considered a turbocharged system to increase high altitude performance but concluded that two-stage supercharged system was better.


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## FLYBOYJ (Jul 19, 2008)

Oreo said:


> And for those of you poo-pooing the use of the Merlin on the P-40-- it is true the speed did non increase much, but the climb rate was up drastically, and so was the service ceiling. And what would keep them from having used a turbocharger system like the P-38 had, for the Merlin engines, rather than the supercharger system? The turbo system was more effective (I guess) in terms of ceiling and high altitude performance.



The P-40 was being used in lower altitudes therefore the Merlin wasn't helping the it's mission role much. The mod to convert the P-38 to Merlin's as pointed out would of been a major undertaking an would of shut the production line down for several months - in mid 1943 when this was proposed the 5th AF was in desperate need for P-38s as they were in critical need in the PTO with regards to AAF operations. Again by the time the late "Js" and "L" models emerged many of the problems were addressed.


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## HoHun (Jul 19, 2008)

Hi Flyboyj,

>The Merlin P-38 never happened because there were no guarantee it was really going to improve anything (look at the Merlin powered P-40s) 

You're going to find a really close look here ...

http://www.ww2aircraft.net/forum/av...e-allison-versus-merlin-14118.html#post376691

(I didn't want to post P-40 data in a P-38 thread ...)

Regards,

Henning (HoHun)


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## FLYBOYJ (Jul 19, 2008)

Just saw that - great info!


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## krieghund (Jul 21, 2008)

Are there any documents that the Merlin was More reliable than the Allison?
I have read after action reports for the P-51A used for low missions over france where the commentator felt that an Allison could bring you home on ruined bearings but a merlin wouldn't. Also read that the packards were stronger than the merlins due to metalurgy.
Just because Allison sat on their hands instead of developing a two-speed super charger doesn't mean the engine isn't any good.
Example is the P-51J

"Ahh, now you've gone and done it!!"


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## Marshall_Stack (Jul 21, 2008)

krieghund said:


> Are there any documents that the Merlin was More reliable than the Allison?
> I have read after action reports for the P-51A used for low missions over france where the commentator felt that an Allison could bring you home on ruined bearings but a merlin wouldn't. Also read that the packards were stronger than the merlins due to metalurgy.
> Just because Allison sat on their hands instead of developing a two-speed super charger doesn't mean the engine isn't any good.
> Example is the P-51J.



I always wondered this myself. It seems like from reading personal accounts from WWII, that the Merlins in P-51s had a high non-combat casualty rate. If this is true (which it may just be my conclusion), there may be other factors in play..


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## FLYBOYJ (Jul 21, 2008)

I had a neighbor who flew P-38s and P-51s in the ETO (some of our older members seen my posts on this, so this is for the sake of our newer members) told me he thought the P-38 made the better G/A aircraft, not only for the two engines but he thought the P-38 was built better than the P-51 and the Alisons could take more punishment.


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## red admiral (Jul 21, 2008)

Theres essentially no difference between the Rolls-Royce and Packard Merlins apart from the supercharger drive and carbs. Reports of differing reliability might not be wrong in themselves, but overall there was nothing between the two. Later models had a difference, with the RR models having more boost and more power but the Packard models with less boost and less power. Reliability improved throughout the war.

The early turbocharged V-1710s were not particularly reliable in Europe, having many many problems. These were to most extents cured with the P-38J in late 1943/44. Then at the end of the war sees the return of the supercharged V-1710 with abysmal reliability when mounted in the P-82.


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## Oreo (Jul 21, 2008)

Don't forget the XP-49. Wasn't that a P-38 with Continental engines mounted?


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## drgondog (Jul 21, 2008)

FLYBOYJ said:


> I had a neighbor who flew P-38s and P-51s in the ETO (some of our older members seen my posts on this, so this is for the sake of our newer members) told me he thought the P-38 made the better G/A aircraft, not only for the two engines but he thought the P-38 was built better than the P-51 and the Alisons could take more punishment.



Joe - there are lies, damn lies and statistics but my current studies show 2x losses of P-38s in strafing losses (all ground attack) to number of aircraft destroyed on the ground vs the Mustang.. I was amazed - and the 51 had about 20% more losses due to flak than P-47. I will say that the losses counted are all forms of strafing and flak and hitting trees etc to a/c destroyed and does not take into account trains, road traffic etc.

The 38 was also weak ( less tha 1/3 the Mustang and 1/2 the P-47) relative to 47 and 51 in air to air ratios.

8th AF FC numbers only


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## kool kitty89 (Jul 22, 2008)

Do you know how pilot losses compare? (ie. taking into account if made it home with an a/c that had to be scrapped)


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## FLYBOYJ (Jul 22, 2008)

drgondog said:


> Joe - there are lies, damn lies and statistics but my current studies show 2x losses of P-38s in strafing losses (all ground attack) to number of aircraft destroyed on the ground vs the Mustang.. I was amazed - and the 51 had about 20% more losses due to flak than P-47. I will say that the losses counted are all forms of strafing and flak and hitting trees etc to a/c destroyed and does not take into account trains, road traffic etc.
> 
> The 38 was also weak ( less tha 1/3 the Mustang and 1/2 the P-47) relative to 47 and 51 in air to air ratios.
> 
> 8th AF FC numbers only



Interesting stuff Bill....

Mike Alba told me that many in his squadron didn't want to give up their P-38s. He said the losses mounted with the Mustang when they went down on the deck.


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