World War II fighter armament: what was too light, what was overkill, what was the Goldilocks zone?

[BarnOwlLover]

To be fair, the USAAF seemed to be looking at countering the Luftwaffe's "Amerika Bomber" program, which it turns out not only happened as far as a serious threat, but was insanely problematic to begin with as far as Germany or Japan getting to work.

In the end, 4 20mm cannons, especially for a single seat, single engine fighter of the 1700+hp class. But it'd take until 1942 for that to happen with the "heavy" fighters of that class (Hawker Typhoon/Tempest or P-47 sized), and it wasn't worth it for say a P-51 or Spitfire sized or powered fighter until 67" Hg/18 lbs of supercharger boost was common place in late 1943 as far as the Merlin power units.

Earlier than that, I'd say that the max for a plane powered by a Merlin or Allison class engine was 2 HMGs and 2 20mm cannons, or 4 LMGs with 2 20mm cannons. Also depends on what you're trying to shoot down or other things you're wanting to do with the fighters.

 

[marathag]

Well, the "lance of steel" seems to be 6.5 mils at 80% (GE literature for the SUU-11B-8 A Minigun pod) and since 6.5mils is about 22 inches at 100 yds (300ft) or 88inches at 400yds (1200ft) I would say that the "lance of steel" may have a bit of flaw.

Vietnam era F-4 pilots noted the SUU-16 and SUU-23 Gatling Pods on the centerline station, were all but useless in air to air, and only good for strafing ground targets. F-8 and F-105 were more accurate with their fuselage mounted cannons

 

[BarnOwlLover]

One thing that I did think of early this morning is that the British (and everyone else in reality) went along with what they had early in the war. The Brits had the .303 Browning, the 20mm Hispano and really nothing in between until they adopted the .50 Browning (early versions weren't that great and the UK didn't have the ammo in the production or supply chain as far as being common until later).

Interestingly, Rolls-Royce tried to design a HMG for the RAF. The Wikipedia article (not sure how accurate it is, though it sites a source published by Rolls-Royce Heritage Trust) does suggest that the weapon was intended to fire .50 BMG, as the RAF wanted a weapon similarly powerful to the AN/M2 .50, but built in Britain. The original recoil operated weapon had functioning issues, and was redesigned to be a gas operated weapon. There was also plans to use the .55 Boys AT rifle round in a rebarreled version.

In the end, Rolls-Royce gave up on it (and a 40mm cannon they were working on) to concentrate on aircraft engine production.

Interestingly, Rolls-Royce did license production of a version of the 40mm cannon to another British company for armament on Royal Navy motor gun boats.

 

[Shortround6]

One thing that I did think of early this morning is that the British (and everyone else in reality) went along with what they had early in the war. The Brits had the .303 Browning, the 20mm Hispano and really nothing in between until they adopted the .50 Browning (early versions weren't that great and the UK didn't have the ammo in the production or supply chain as far as being common until later).

Interestingly, Rolls-Royce tried to design a HMG for the RAF. The Wikipedia article (not sure how accurate it is, though it sites a source published by Rolls-Royce Heritage Trust) does suggest that the weapon was intended to fire .50 BMG, as the RAF wanted a weapon similarly powerful to the AN/M2 .50, but built in Britain. The original recoil operated weapon had functioning issues, and was redesigned to be a gas operated weapon. There was also plans to use the .55 Boys AT rifle round in a rebarreled version.

In the end, Rolls-Royce gave up on it (and a 40mm cannon they were working on) to concentrate on aircraft engine production.

Interestingly, Rolls-Royce did license production of a version of the 40mm cannon to another British company for armament on Royal Navy motor gun boats.

Many countries used what they had and then progressed to what they were planning/developing before the war. It often took 3-6 years to bring a gun from initial concept to working squadron service. This last is somewhat debatable as the US .50 was supposed to have been used for pretty much all of the 1930s and yet it didn't work for the British in 1940 and early 1941 for the British is several different aircraft. The German MG 131 and the MG 151 were both in development in late 30s.
You also have to tool up a factory to make the guns and another factory to make the ammunition. Or buy the ammo from an other country. And you have to print the training manuals and train the armorers before you try to issue the guns to service squadrons.
Britain wanted a 2nd source for a .50 cal Machine gun, however, as these things often do, certain people just didn't want to copy the existing weapon, they wanted "improvements".
Like a shorter, lighter weapon that was more suitable for turret installation. As a note here, the US made under 8,000 50 cal guns in 1940 so there weren't enough to go around for the US Army, the US Navy, the US Air Corp and the British. Things improved by an order of magnitude by late 1941 and in 1942 they were cranking out well over 100,000 a year.

The RR gun cut the barrel by 5in which helped with size and weight but that increased muzzle flash so they had to put a sizeable flash hider on it which pretty much canceled the shorter length. The RR gun was supposed to fire faster but it never completed development so who knows? The gun, according to one source, was supposed to weigh 49lbs, The receiver was made of a proprietary RR alloy, which may or may not have affected production at a later date. One source gives a rather low velocity, but since the British were using the M1 Loading with a velocity of 2500fps in 1940-41 cutting the barrel shorter may have cut the number to the value given?
Changing to the .55 Boys seems to be an unneeded complication although it may simply have overlapped the progress of the US .50 cal ammo.
By the time the RR machine gun was under development they had cut the weight of the .55 Boys bullet to increase the velocity and the resulting bullet weight and velocity wasn't much different than the .50 cal M2 load (and it's variations).
But for the British in late 1941 or early 1942, they don't have a factory set up, they are not set up to make ammo in machine gun quantities, not AT rifle quantities. US .50s are showing up in numbers, and aircraft designers (or least fighter designers) are figuring out 4-6 gun 20mm planes and the gun designers are figuring out faster firing 20mm guns.

As far as the RR 40mm gun goes. There seems to be a large difference of opinion between the Wiki site and another reputable source (Mr. Williams), It seems to have been not as good as the Vickers S gun and later in timing. The touted use on MTB/MGBs as an AA gun needs a little explanation. As a gun against enemy small craft it may have been quite useful. As an AA gun? The thing weighed about 3 times as much as an Oerlikon and was mounted on the same pedestal. It fired semi-automatically (gun fired and ejected the spent cartridge and then remained open until the loader rammed the next round into the breech at which point the breechblock slammed shut) in this mode the gun fired at about 30rpm at best instead of the 114rpm (?) of the magazine fed aircraft gun. You could shoot it at airplane and it may have been marginally more effective than the boat crew simultaneously raising a one finger solute to the attacking plane but not much. It may have been better for morale.
The 40mm gun went through BA to BH versions (with a few skips) and the BH versions received 4 mark numbers, there seems to be no information on the MK III and the MK IV was belt fed after the magazine fed MK I & II.

 

[tomo pauk]

I'm trying to see or at least get opinions on armament that was too light, too much, and just right for World War II fighter aircraft. I'll be splitting this into the 1939-42 and 1942-15 eras, and will be taking into account fighter vs fighter and fighter vs bomber/recon aircraft scenarios. This will of course take into account caliber of weapons, prospective roles (strafing included), and ammo capacities/firing time.

Anyone have any idea of what did/didn't work here, as well as what was over the top?

For the 1st era, there was a number of fighters with battery ranging between two LMGs and two HMGs, those are probably too lightly armed fighters. MiG-1/-3 is barely better.
The US insistence on 6 MHGs for the F4F-4, P-40E and the like, as well as the 7 gun battery on the P-39D and the like produced fighters with abysmal performance (it also had a lot to do with meagre power increase, if any; the overboosted V-1710s notwithstanding). The 4-cannon Hurricane was with the similar problems - fine/excellent firepower, low performing fighter.
Other fighters are probably in the middle? Some of them were with guns' setup that left something to be desired, like the Bf 109E-3 (too much disparity between the MVs of the 4 guns), low ammo count for most of the cannons before 1941, dubous utility of the American 37mm gun, reliability issues etc.

Past 1942, the weakest batteries are on Soviet fighters and many of the IJA fighters. On what Fw 190A-7 and later Antons were carried, we can say that it was too heavy and too draggy, while still not deemed good enough to kill the 4-mots? American batteries of 6-8 HMGs are sufficient to the job, and there is enough of horsepower to carry these (bar on the P-40s); but indeed, Americans were not fighting sturdy bombers like the Axis had to do. British 4 Hispano battery (even better if it is the Mk.V) on Tempest and Typhoon seems excellent to me, since there is a lot of HP to lug these around.
Again the Bell fighters are meh in this regard.

 

[BarnOwlLover]

This is why I split this into two eras. 1942 marks the widespread introduction of the two-stage Merlin (and also starting to increase boost on the single stage versions), the widespread use of the Fw-190, the combat introduction of the P-51 Mustang, the ramping up of production of the P&W R-2800 and the R-R Griffon, etc.

In the end, even the Merlin was making a lot more power than I think even the two stage version was envisioned to make, even during the war. "Just" 18 lbs/67" boost enabled the Merlin Mustangs at combat weight to fly at over 450 mph and have 4200+ fpm initial climb rates. The Spitfires with those same engines were slower in terms of top speed, but could climb at nearly 5000 fpm. Granted, this isn't really until late 1943/early 1944 that this started to happen, and we didn't see Merlins go boosted to 25 lbs/80" until Mustang IIIs, some Merlin Spitfires and quite a few Mosquitos be used to intercept V-1s. These figures are WEP/combat ratings, and basically required 145 octane fuel to make full use of them (especially higher ratings), but the Allies did have that ability by then.

And of course, more power does mean that you can carry more weapons/heavier weapons and maybe more ammo. That's why the P-51H was basically a hybrid of the LW F/G models with the D model. The desire for similar performance, but with heavier armament and above all else, more internal fuel (other than lengthening the fuselage and restressing for designed G load at a higher normal max gross weight those were the biggest changes).

Even the outlier F-82 as tested in XP-82/P-82B format (which like the DH Hornet and pretty much the P-51H itself missed the war) did reach a 4900-5000 fpm climb rate (not sure on what power figures or weights or fuel capacity--I haven't gotten a good look at the SAC documents, and none are available at least as of yet at least at World War II Aircraft Performance). But as I said, it and other very late war aircraft that saw little to no use are basically outliers at this point.

And it stands to reason as available power went up, armament increased. Also at the same time, that meant (in theory) bomber aircraft would get larger and faster, though this didn't really happen for the Axis (at least until it was too late to make much difference).

 

[A.G. Williams]

One thing that I did think of early this morning is that the British (and everyone else in reality) went along with what they had early in the war. The Brits had the .303 Browning, the 20mm Hispano and really nothing in between until they adopted the .50 Browning (early versions weren't that great and the UK didn't have the ammo in the production or supply chain as far as being common until later).

Interestingly, Rolls-Royce tried to design a HMG for the RAF. The Wikipedia article (not sure how accurate it is, though it sites a source published by Rolls-Royce Heritage Trust) does suggest that the weapon was intended to fire .50 BMG, as the RAF wanted a weapon similarly powerful to the AN/M2 .50, but built in Britain. The original recoil operated weapon had functioning issues, and was redesigned to be a gas operated weapon. There was also plans to use the .55 Boys AT rifle round in a rebarreled version.

In the end, Rolls-Royce gave up on it (and a 40mm cannon they were working on) to concentrate on aircraft engine production.

Interestingly, Rolls-Royce did license production of a version of the 40mm cannon to another British company for armament on Royal Navy motor gun boats.

This is the book you need - highly recommended: Rolls-Royce Armaments: Amazon.co.uk: Birch, David: 9781872922157: Books

 

[drgondog]

NAA and RAF always wanted 20mm. Not available during early years of Hispano II licence. After 1942, AAF consistently rejected 20mm proposals from NAA, including A-36 P-51F and RAAF Mustang. Ditto F-86 until enough returning warriors described hammering migs - 'but no fires at 37000 feet' with many getting away. Gunval finally convinced USAF.

PS - I have talked to more than acouple of LW pilots that were happy that P-51 didn't have 20mm.

 

[BarnOwlLover]

I wonder if the USAAF ignored 20mm because of problems with production (especially wing mounted cannons) due to (allegedly) building to improper tolerances, or the fascination with their own .60 HMGs, or the upcoming M3 .50 BMG?

It doesn't help that due to increasing speeds and stresses, the F-86 and MiG-15 were built to higher stress standards and strength than most World War II fighters. And IMO, 20mm could've been a big boon for the P-51, P-47, P-38 (more 20mm than one in this case), P-82, and USN aircraft (who took 20mm a lot more seriously it seemed).

 

[Shortround6]

Ditto F-86 until enough returning warriors described hammering migs - 'but no fires at 37000 feet' with many getting away.

And there is the difference between theory and reality.
The F-86 was putting out about 50% more bullets than the WW II 6 gun fighters.
The Bullets were also a lot faster than WWII bullets....................however.

They were also a lot lighter, the M23 weighed about 512 grains (33.11 grams) or about what the German 13mm bullets weighed.

They may have penetrated a single layer of metal fairly well (don't know, just speculating) but going through heavy fuselage or wing skinning and then going through stuff doesn't look good. The WW II M2 AP and M8 API had substantial chunks of heat treated alloy steel in them. They were also known for going sideways after hitting things (like skin) but at least you had the large chunk of steel hitting things inside the plane. The M23 is going to break up and scatter the incendiary material either on the skin or just inside and apparently, no matter how good it did at setting fire to things at low altitude, it didn't work well in the thin air at 37,000ft or above.

Now the problem the USAAF had was that the M23 is unlikely to hit where all the other types of ammo are going to hit due to the different velocity (150-180m/s) and weight of the bullets. The F-86 used a more sophisticated sight system (range setting radar in the lip of the nose) so there was more than just swapping in belts of old ammo.

If they didn't run tests at 37,000ft to see if it would set fire to stuff perhaps they didn't know ??

 

[Thumpalumpacus]

Another armament loadout I love, though not mounted on an air-superiority fighter, is the Beaufighter's 4 20s in the nose and 6 .303s in the wings. That thing scared ships.

 

[Shortround6]

While it was post-war I would note that the US Air Force never deviated from the 20mm guns in purpose built Night-fighters. From the P-61 to missiles the Night fighters and early all weather interceptors (F-89s) had four 20mm cannon and later six 20mm cannon.

Adapted fighters to the night fighter mission (P-38s with radar pods) kept most or all of their original armament. US Navy night fighters are their own path of development.

 

[z42]

The M23 is going to break up and scatter the incendiary material either on the skin or just inside and apparently, no matter how good it did at setting fire to things at low altitude, it didn't work well in the thin air at 37,000ft or above.

Also, jet fuel is significantly less flammable than gasoline. Though at the time IIRC everyone (except USN?) was using wide cut kerosene which is more flammable than the narrow cut kerosene used today.

 

[drgondog]

While it was post-war I would note that the US Air Force never deviated from the 20mm guns in purpose built Night-fighters. From the P-61 to missiles the Night fighters and early all weather interceptors (F-89s) had four 20mm cannon and later six 20mm cannon.

Adapted fighters to the night fighter mission (P-38s with radar pods) kept most or all of their original armament. US Navy night fighters are their own path of development.

I think the F-94 left the barn with 50 cal? Ditto F/P-82. The E & subsequent were definitely purpose built as all weather/night fighter

 

[Shortround6]

I think the F-94 left the barn with 50 cal? Ditto F/P-82. The E & subsequent were definitely purpose built as all weather/night fighter

We may be splitting hairs.
F-94 was a modified TP-80C/TF-80C/T-33. Yes it left the barn with just four .50cal mgs but there was only so much room in the stretched P-80 airframe once you stuffed in the 2nd seater and radar/fire control unit.

The F-82C (10th F-82B airframe) and F-82D (11th F-82B airframe) became the prototypes for the for F-82F and F-82G after the F-82E (escort fighter, not night fighter?) switched to the Allison engines. Now perhaps the Night fighter versions had been planned all along and the escorts just had more priority but aside from grafting the radar pod under the wing center section and converting the starboard cockpit to be the radar operators station they don't seem to have changed much else.
I have no idea what NA was planning in the design rooms vs what the Air Force ordered in the early stages of the design, but six .50s with 300rpg was pretty weak stuff for a night fighter.

 

[BarnOwlLover]

F-82s had 400 rpg as far as production aircraft and even the XP-82s it seems (XP-82 Restoration team did load 400+ rounds for each of the 6 50s in their XP-82). But I've read different things regarding especially the P-51H that varied between 4 .50s, 6 .50s, 4 .60s and 4 20mm. This is per post on secretprojects. And also per post, it was the USAAF looking at this, but it was seemingly NAA that favored the 6 .50s. Which wouldn't surprise me if true. Because in the past, NAA wanted to put 20mm cannons on P-51s and A-36s, as well as even 37mm cannons on the A-36. But the USAAF ignored such proposals and favored the .50s.

 

[drgondog]

We may be splitting hairs.
F-94 was a modified TP-80C/TF-80C/T-33. Yes it left the barn with just four .50cal mgs but there was only so much room in the stretched P-80 airframe once you stuffed in the 2nd seater and radar/fire control unit.

If you can squeeze 20mm into F-86, can't find design reason that they wouldn't fit in an F-94?

The F-82C (10th F-82B airframe) and F-82D (11th F-82B airframe) became the prototypes for the for F-82F and F-82G after the F-82E (escort fighter, not night fighter?) switched to the Allison engines. Now perhaps the Night fighter versions had been planned all along and the escorts just had more priority but aside from grafting the radar pod under the wing center section and converting the starboard cockpit to be the radar operators station they don't seem to have changed much else.
I have no idea what NA was planning in the design rooms vs what the Air Force ordered in the early stages of the design, but six .50s with 300rpg was pretty weak stuff for a night fighter.

The auxilliary /recon weapons pod added 8x50 cal for additional firepower, which was introduced with the E. You are correct tha the E was the last non radar equipped escort version of the P/F-82. That said, the F & G could have moved from all weather night fighter to LR escort had the need arisen with war against either USSR/China circa 1950.

Nothing had the range through even today to match the P/F-82 for either escort or NF once the P-61 was retired, and even the P-61C, which never entered service, could have escorted @ B-29 fast cruise at 30,000 feet.

That said, even for night missions the F-82G with radar would have been a poor match for Mig 15. Offhand, I don't know what the Soviet NF equipment looked like in 1950-54.

But could be splitting hairs..

 

[Shortround6]

If you can squeeze 20mm into F-86, can't find design reason that they wouldn't fit in an F-94?

Well, timing for one thing, how long does it take to design the new armament installation.
Not saying it can't be done, but complicated vs simple takes time.
Then there is the question of which F-94 and which F-86, not so simple.
The F-94A was a pretty simple take a T-33 (or the then current F-80 trainer) and stuff the radar into the nose and the use the rear seat for the radar operator. Engine power was not great and neither was reliability and they cockpit space was tight and ejection was not the best.
F-94B was better (improved J-33 engine) and had a better cockpit. They did offer the option of under wing gun pods to raise the total guns to eight .50s.
F-94C, another funding trick of the era. . Yes Congress, it is just a modified F-94 (don't tell them it has a new wing, new tail, new fatter engine that needs a partially new fuselage and a new weapons system). Maybe they could have yanked the rockets and stuffed in guns?
Early F-94

the gun muzzles are in the shark mouth under the radar dome. You do have a CG problem and a gun gas ingestion problem, Not saying they can't be fixed but the idea was to get a radar equipped jet night fighter in a hurry while working on the F-89.

F-86 went through some changes of it's own. But even the "night fighter" versions were single seat. The night fighters only had about 25% commonality (?) with the standard Sabres.
The F-86s with 20mm guns had less to contend with. Picture is of a F-86H.

less chance of gas ingestion and guns/ammo closer to the CG.

That said, the F & G could have moved from all weather night fighter to LR escort had the need arisen with war against either USSR/China circa 1950.

They could have. My point was that the 'as designed' night fighters had 20mm guns. The 'modified' night fighters generally had the same guns as the parent aircraft.
P-70s flipped back and forth.

 

[drgondog]

F-82s had 400 rpg as far as production aircraft and even the XP-82s it seems (XP-82 Restoration team did load 400+ rounds for each of the 6 50s in their XP-82). But I've read different things regarding especially the P-51H that varied between 4 .50s, 6 .50s, 4 .60s and 4 20mm. This is per post on secretprojects. And also per post, it was the USAAF looking at this, but it was seemingly NAA that favored the 6 .50s. Which wouldn't surprise me if true. Because in the past, NAA wanted to put 20mm cannons on P-51s and A-36s, as well as even 37mm cannons on the A-36. But the USAAF ignored such proposals and favored the .50s.

I have not seen any documents, including proposals, that cite 20mm for P-51H. The one 'inferred' possibility was 1945 Propsal to USN for P-51H carrier qual version. That said, even the NAA FJ-1 was delivered with 6x50 cal as the USN had not yet settled on all 20mm armament.

EDIT Follow up. Putting an Oldsmoble 20mm would force NAA to beef up the forward spar, as designed, to acomodate the larger envelope. The Browning breech fit nicley between fwd and aft spar, with only barrel punched through an appropriate lightning hole.

The same issuse existed with arming P-51F with Oldsmobile cannon.

 

[BarnOwlLover]

There's this post on secretprojects from someone who was researching later P-51 developments, though he doesn't cite sources (and I even asked for further info later in the thread):

P-51 Mustang & F-82 Twin Mustang Proposals and Variants

All the better ! I think, we'll see it in the mentioned future APR issue ?

www.secretprojects.co.uk

Even if the USAAF was looking for alternatives, if I was North American, and having been burned when proposing anything more than .50s on P-51s and A-36s previously, I'd have designed at least provision for 6 .50s from the start. Also, it was seemingly the USAAF that asked for heavier armament (6 .50s at least instead of 4, 1000 lbs of bombs under each wing, 10 HVARs, more internal fuel as well) that lead to the evolution of the XP-51F/G to the P-51H.

That said, there's photos of the NA-117 mock up (as the P-51H was known as until it became the NA-126) featuring what look like Hispano cannons being mounted in the wings, with two per wing. So it seems that NAA did expect possible armament changes, be it from the USAAF or maybe an export customer.

And one of the few papers I've seen cited for the NA-133 development called for 6 .50 MGs with 300 rpg in the intended or envisioned specs:

North American NA-133 - Navalized P-51H Mustang.

So buried in the Spangenberger Index at NARA was a folder on the XF8B and the North American Liquid Cooled VF; which I found thanks to Stargazer's excellent finding aid. And my guess as to what the NAA Liquid VF was turned out to be correct. There were no eye popping brochures, but a mass of...

www.secretprojects.co.uk

Also hoping that you find enough info to include the XP-82/Merlin P-82 in your book about the Lightweight Mustangs, though I'm not holding my breath unless some archive has the info you want/need or maybe AirCorps Library has it in their NAA documents or the XP-82 Restoration Project has them (someone did send them a copy of the XP-82/P-82B SAC documents--I tried to read the info on the page they posted a photo of, but couldn't make anything out).