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

[BarnOwlLover]

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?

 

[Shortround6]

armament that was too light

Light in regards to weight of the guns/ammo?
Light in weight in regards to weight of projectiles per second (firepower).
They are not always the same thing.
Also sights varied a bit. Not everybody was using reflector sights in the early part of the war.

 

[BarnOwlLover]

Either or both, and as I said, it would probably vary by era and probably role. And I'm looking at this as far as "suit all comers" issue. For instance, even multiple rifle caliber MGs would be "light" for dealing with most bombers after 1940 (if not earlier), but using a 37mm cannon to shoot down fighters at almost any point in the war could be considered "overkill".

Also there's the issue of ammo capacity. How much firing time is good enough vs carrying too much. Was the P-47N carrying 8 .50 MGs with up to 500 rpg too much? Were most USN naval fighters post 1942 ( 6 .50s with 400 rpg) overkill? That was 30 seconds worth of firing time.

I don't know about the 1939-42 era yet as far as my opinion, but from '42-45, it'd be between for a GP role either 6 .50s, 2 .50s and 2 20mm cannons, or 4 20mm cannons, ammo capacity to be determined.

But it does seem that the US did kind of like giving their planes lots of ammo. I gave two examples above, but even when 20mm cannons were looked at, they gave them usually at least 200 rpg in say the P-61, as well as cannon armed F4Us, F8Fs and prospective fighters like the Convair XP-81 and the Boeing XF8B. I know that the Lavochkin La-5 and La-7 carried 200 rpgs for their 20mm cannons, but they carried only 2 of them and they were the only gun armament carried (aside from some La-7s that had 3 cannon, which got trimmed to 100 rpg).

 

[Shortround6]

For instance, even multiple rifle caliber MGs would be "light" for dealing with most bombers after 1940 (if not earlier), but using a 37mm cannon to shoot down fighters at almost any point in the war could be considered "overkill".

Well, to pick up some of the extremes, the British/US small Browning'1s went 9.8-10,4kg while the early Hispanos went about 50kg (without feed system) and the US 37mm went 96 kg.
So we do have quite a range.
However the 37mm wasn't that useful as a anti-fighter gun. It fired at about 2.5 rounds per second so while a single hit was devastating, getting the hit was rather difficult. Also note that US 37mm shells had a MV of 610m/s so it needed a bit more lead was needed than most other guns. Please note that the US .50 cal fired at 880m/s veleocity so time of flight was shorter. Russians generally fired at very close range to minimize this. The 37mm also held 30 rounds of ammo. 12 sec which isn't bad but but in terms of ammo fired into the target area per second is...................1.525 kg/sec. A single 20mm HS fires 1.28kg/sec. As noted above the 20mm gun was almost 1/2 the weight. Eight .303s will fire about 1.60 kg/sec.

Were most USN naval fighters post 1942 ( 6 .50s with 400 rpg) overkill? That was 30 seconds worth of firing time.

We are getting into the 2000hp engines, which changes things
F4F-4 with six guns used 240rpg, and had 18 seconds firing time which is within 2 seconds of the firing time of the Hurricanes and Spitfires.

 

[BarnOwlLover]

One aircraft that I think is an outlier is the P/F-82, which had two engines of between 1800-2200+ hp (depending on power setting), and it carried 6 .50s with 400 rpg. You cut it in half, you get an aircraft that was similar in weight to the P-51H (powered by the same engine, just one of them). That carried 6 .50s with 390/260/260 rpg going from inboard to outboard.

Which was the better fit for say a single seat, single engine fighter? It should be noted that the P-51D when carrying 6 .50s had 400/270/270, and the P-51B had 4 .50s with 350/280 rpg.

And for the most powerful Spitfires, those carried 4 20mm cannons, but with 175/150 rpg.

 

[Thumpalumpacus]

I like the P-38 simply for the weapons layout -- concentrated and no synchronization. 20mm and four .50s was definitely adequate for most of the war and most of its opponents.

 

[ThomasP]

For the US and UK late-war period another break point would be pre- and post-GGS (Gyro Gun Sight).

Pre-GGS = more guns, higher MV, and higher ROF are better
Post-GGS = while the above are still important, single hit effects become a bigger part of the equation, so guns of 20mm and larger are better

From what I have read the GGS increased the chance of a hit by somewhere around a factor of 3.

 

[Shortround6]

One aircraft that I think is an outlier is the P/F-82,

I don't know why we are discussing the P/F-82 in a thread about WW II aircraft.
I understand it is something of a fan favorite but it is so late in timing that only 2 airframes flew before Japan surrendered. The P-82E/F were not even ordered until Oct 1946 (?) and didn't fly until 1947/48.
It should be on the USAAF '46 pages to counter the Luft 46 pages on the web.
Sources seem to say that the P-82 used M3 .50 cal guns and not the M2 guns used in WW II. The M3s fired at 1100-1200rpm and would have the firepower of nine of WW II M2 guns.
They may have used different ammunition also or planed to use different ammo. The US had quite a bit of difficulty getting the new ammo into service (troop trials in Europe in very late 44 or early 45) but they were still having trouble with it in Korea. They had changed manufacturing facilities twice to try to get better quality control between 1944 and 1950. Planned use vs actual use was all over the place.

 

[BarnOwlLover]

I'm going to bring up a point that drgondog brought up in a thread of where I asked about the P-51D vs P-51H and XP-51F/G as far as performance and timing. The lightweight Mustang project started in early 1943, and the initial proposal that led to the F-82 began at about the same time.

In the timeline as we know it, the P-51D was generally more than sufficient from a performance standpoint. But North American nor the USAAF knew that Germany would surrender in May of 1945, and Japan in August of that year for most (if not all) of 1944, let alone 1943. Hence why work on those projects continued, with the XP-51F/G evolving into the P-51H program from early 1944. Also, the P-80 and Meteor and Vampire jets pressed ahead even though Axis defeat became imminent in '45. And those programs started even earlier than the P-82 and the P-51H/XP-51 programs.

Point there being that even if the war went on only say 6 months longer in either theater, all the planes I mentioned (and probably others) likely would've seen some use. Even the P-51H never saw any (at least confirmed) combat ops against Japan, though they were in USAAF inventory, were starting to be delivered to units, and over 370 got made before VJ day (order ultimately cut to less than 200 additional aircraft after that point for a total of 555). Even the P-47N saw little use in the Pacific prior to war's end.

But back on subject, we know that the USAAF didn't seriously invest in 20mm cannons for most fighters because of issues with the US made versions of the HS-404, especially in wing mounts (which was also an issue at times with the .50 Browning, especially in P-51s until the D model). I've read that the USN for both ground attack and interceptor/counter-air work wanted cannons, but never really got them until very late in the war or post war. Of course, things may've been different if we built our versions of the HS-404 to British specs, as the Brits largely stopped having trouble with them when the Mk II version came out.

Of course, the Germans went berserk as far cannon armament for fighters, equipping Me-109s and Fw-190s with 30mm cannons, the Me-262 with 4 30mm cannons and even 37mm and 50mm cannons in some of their twin engine fighters. Granted, aside from the occasional He-177 raid, the British mostly dealt with twin engine medium bombers, and the US was never bombed by either German or Japan as far as the mainland went. And though say the 190 did OK with such things (until being chased around by a P-51, P-47 or P-38), the Me-109 can be said as being too small for it's own good as a bomber destroyer, as the heavier weapons def. hurt it's performance very badly in terms of speed and handling. Even the 190 didn't cope that well when it had to engage in fighter vs fighter combat with such heavy armament.

The other point I want to look at is firing time. For 6 .50 MGs with 400 rounds a gun, that's 30 seconds of firing time (about 20+ seconds with the faster firing M3s) If all 6 .50s on a P-51D were loaded with 270 rounds (standard capacity for the outboard 4), that'd be almost 20 seconds of firing time. I did read on here somewhere that the ideal firing time for most aircraft guns in World War II was 15-18 seconds plus or minus 1-2 seconds or so. Spitfires with 20mm cannons with 120 rpg had a firing time of about 11-12 seconds (Hispano Mk II).

The Hawker Tempest V had Hispano Mk Vs (lighter and faster firing) with 200 rpg for it's quad of them. But the Mk II Tempest had 162 (inboard) and 156 (outboard), and the stillborn Tempest I had 150 rpg.

So maybe I guess I'd like to know the best for hitting power (without over-doing it), best for firing time, and maybe the best compromise.

 

[Shortround6]

But back on subject, we know that the USAAF didn't seriously invest in 20mm cannons for most fighters because of issues with the US made versions of the HS-404, especially in wing mounts (which was also an issue at times with the .50 Browning, especially in P-51s until the D model). I've read that the USN for both ground attack and interceptor/counter-air work wanted cannons, but never really got them until very late in the war or post war. Of course, things may've been different if we built our versions of the HS-404 to British specs, as the Brits largely stopped having trouble with them when the Mk II version came out.

I think it took a bit longer for the British to really sort out the Hispano gun. Getting it to acceptable reliability was one thing. Getting good reliability may have taken more work. Remember that they were using the Hispano for about 4 years.

For the US the actual records/memo's seem to be rare as to what they were thinking. They were certainly planning a host of different projects, most of which never left the experimental shops. .60 cal machine guns, .50/.60 cal cartridges, 20mm shells firing .50 cal bullets and more. Trying to sort out what the imagined benefits were without written explanations gets hard.
The US was smart enough not to try to ship small batches of guns/ammo thousands of miles across oceans for experiments.
The Navy was looking for more destructive power. They wanted enemy bombers shot down NOW, before they could drop bombs/torpedoes. The Army seemed to be chasing the high velocity goal, They estimated the increased velocity would decrease the time of flight and increase hits while deflection shooting due to not having to lead the targets as much. Trouble was that the gun/ammo weight when up (way up) and barrel life, not good with .50 cal, got even worse.

But there don't seem to be any memo's that say why they did something at a certain date, at least for the Army. The Navy seems to have given up on the .50 cal in fall of 1944. No new fighter contracts were signed for fighters using .50 cal guns after that time. Now delivery could still be a year or more (2-3 years) in future.

This may have been the last Navy fighter planned to use .50 cal guns? First flew in Jan 1945 (with one engine) and didn't enter service until 1947.

 

[pbehn]

One aircraft that I think is an outlier is the P/F-82, which had two engines of between 1800-2200+ hp (depending on power setting), and it carried 6 .50s with 400 rpg. You cut it in half, you get an aircraft that was similar in weight to the P-51H (powered by the same engine, just one of them). That carried 6 .50s with 390/260/260 rpg going from inboard to outboard.

Which was the better fit for say a single seat, single engine fighter? It should be noted that the P-51D when carrying 6 .50s had 400/270/270, and the P-51B had 4 .50s with 350/280 rpg.

And for the most powerful Spitfires, those carried 4 20mm cannons, but with 175/150 rpg.

I think the increase in ammo per gun on the P-51D was dependent on improved feed mechanism, which also prevented jamming.

 

[marathag]

23mm Madsen was a missed opportunity for the US.

 

[Thumpalumpacus]

23mm Madsen was a missed opportunity for the US.

I've heard of this used on P-38s, but know little about it. Might you give a "for Dummies" rundown on the benefits/drawbacks of it?

 

[marathag]

I've heard of this used on P-38s, but know little about it. Might you give a "for Dummies" rundown on the benefits/drawbacks of it?

Madsen USAAC test before the War.
The Madsen 23mm had much more explosive filler than most other 20mm rounds, it was an early type of what the Germans called a Minengeschoß, a Mine Shell for the FF cannon to make them more effective. It had 17 grams of filling, vs 5 grams for standard HE

The Madsen 23mm had 17grams filling and a MV of 730m/s, and was belt fed from the start, so the fun with drums is avoided from the start, though drums were an available option.

Was Recoil operated, 117-121 pounds in weight, 79" OAL and 400 rpm

 

[Thumpalumpacus]

View attachment 735222View attachment 735223View attachment 735224
Madsen USAAC test before the War.
The Madsen 23mm had much more explosive filler than most other 20mm rounds, it was an early type of what the Germans called a Minengeschoß, a Mine Shell for the FF cannon to make them more effective. It had 17 grams of filling, vs 5 grams for standard HE

The Madsen 23mm had 17grams filling and a MV of 730m/s, and was belt fed from the start, so the fun with drums is avoided from the start, though drums were an available option.

Was Recoil operated, 117-121 pounds in weight, 79" OAL and 400 rpm

Thanks for taking the time to lay it out for a plebian like m'self. Mucho appreciado.

 

[Shortround6]

The increase in shell weight goes up with the cube of the diameter so a 23mm shell should be about 50% heavier than a 20mm shell of the same shape. The 23mm maybe a bit short as it was intended to to be able to swap barrels on the same mechanism to change calibers so the overall length of the of the two cartridges had to be similar. The 23mm case was shortened about 14mm so that there was a bit more room for the projectile.

The Madison was used on a couple of US aircraft sold to foreign countries in small numbers.

The Madison had a few problems compared to the Hispano.
One was that the Madison was pretty much a scaled up Madison MG which used a swinging breechblock (hinged on one end) instead of a reciprocating bolt. It was not easy to machine. The advertisements posted by Marathag claim 400rpm which is about 2/3rds that of the Hispano and the velocity was about 1/2 way between the small Oerlikon and the Hispano.

Edit.

Madison Mechanism. Getting it feed from a belt is a real trick.

 

[BarnOwlLover]

One thing that I did read on Secret Projects site is that the USAAF were looking at armament fits for the P-51H and maybe the P-82 for their anticipated use in the Pacific Theater. The USAAF, at least for the P-51H was looking at 4 .50s, 6 .50s, 4 .60s, or 4 20mm cannons (the heavier of the 3 options being looked at for the P-82 I'd guess). In the end, the USAAF did favor 4 20mm cannons, but it seems that North American got their way in the end with the 6 .50s because that's what they spent the most time working on, as well as the fact that NAA did look at 4 20mm cannons even for the P-509 (design study that when scaled up became the NA-73X/P-51/Mustang I), and they looked at 20mm, 37mm and a mix of the two for the A-36, but the USAAF favored 6 .50s for it.

Also according to drgondog, the USAAF was looking at arming the XP-51F (if adopted as an interceptor) with 4 20mm cannons as well as having the 4 .50s as an option. There's also pictures of the NA-117 (a mock up of the P-51H before it became the NA-126 when a production contract was signed) being armed with 4 Hispano cannons. They were just mock ups, but I'd guess that they were 20mm. But then again, the .60 MGs were based on the Mauser MG151, the HS-404, and even the .50 Browning MG.

 

[marathag]

The increase in shell weight goes up with the cube of the diameter so a 23mm shell should be about 50% heavier than a 20mm shell of the same shape. The 23mm maybe a bit short as it was intended to to be able to swap barrels on the same mechanism to change calibers so the overall length of the of the two cartridges had to be similar. The 23mm case was shortened about 14mm so that there was a bit more room for the projectile.

The Madison was used on a couple of US aircraft sold to foreign countries in small numbers.

The Madison had a few problems compared to the Hispano.
One was that the Madison was pretty much a scaled up Madison MG which used a swinging breechblock (hinged on one end) instead of a reciprocating bolt. It was not easy to machine. The advertisements posted by Marathag claim 400rpm which is about 2/3rds that of the Hispano and the velocity was about 1/2 way between the small Oerlikon and the Hispano.

Edit.
View attachment 735227
Madison Mechanism. Getting it feed from a belt is a real trick.

I think it was in one of Ian Hogg's books on machine guns not remarkble that it was a very solid and reliable MG, but that it worked at all. Not bad for an operating system patented in 1899

Spoiler: Gun Jesus showing on how the Madsen action works

View: https://www.youtube.com/watch?v=zpF2hS2avd8

Neither the cartridge or the gun was perfect, but would have been a working solution for the early-mid war period.
It had a very short receiver for a 20mm cannon cartridge, though was far deeper than most

 

[A.G. Williams]

This might be of interest: WORLD WAR 2 FIGHTER GUN EFFECTIVENESS
or this: IDEAL WW2 FIGHTER ARMAMENT

 

[Geoffrey Sinclair]

Agreeing with others. What is the usual target? Piper Cub, B-29, Tiger Tank?

The USN found it needed to upgrade its AA armament for Kamikazes which had to be blown out of the sky, not just shot down and continue on a ballistic path until crashing (into a ship).

When attacking bombers what is their defensive armament? A pair of 0.50 inch machine guns was about as dangerous to a multi cannon armed fighter as the fighter was to a heavy bomber, a bomber with rifle calibre machine guns enabled the fighter to come to closer range before the lethality was balanced.

The RAF went through a machine gun versus cannon debate in 1940/42 initially units expecting to encounter fighters wanted machine guns retained, those expecting bombers wanted cannon.

Generally the higher the aircraft weight the more hits/damage needed to bring the aircraft down, the average aircraft weight in each category grew during WWII.

For air to air high muzzle velocity reduces deflection shooting problems but ups gun weight. High rate of fire ties into aiming accuracy, the more firing time the more time the pilot has to correct aim but the more ammunition weight carried. You want high rates of fire when hitting, but not when missing and most shots missed. Bigger calibre equals more weight so less guns and ammunition but more lethality when hits are scored. Explosive shell hits usually create more damage than solid shot.

The Browning 0.5 inch machine gun was just about perfect for what the USAAF encountered in WW2, it would not be its fighters armement if the USAAF was tasked with shooting down B-17, B-24 and B-29.