Maneuverability vs Speed

[PAT303]

I know they had some trouble with the cannon, but i also know the cannon worked, which is why basically every nation except the US switched over to 20mm cannon on every fighter. As 'superlative' as the eight (lmg) gun armament was supposed to be, it didn't last too long in the world of fighter design

The one thing the the 303 Browning did in 1939 was work as did it's ammunition, it took many years to get the .50 cal Browning and various 20mm's to the same level of reliability, as for lasting very long, if I was fighting against A6M's I'd happily take the eight MG's, four with AP four with De Wilde all zeroed at 200m.

 

[PAT303]

Pilot armor and self sealing fuel tanks were good to have, but their importance is sometimes exaggerated.

I've read some rubbish in my time but this takes the cake, every country, EVERY country, even Japan fitted protection to their aircraft after the experienced and realisation of what an actually shooting war is like, often to the detriment of the aircraft's performance yet you think it's exaggerated?.

 

[PAT303]

Read the operational histories.

Do you think the pilots of these Spitfires think pilot protection is overrated?.

 

[yulzari]

To be fair, the Mosquito was both a fighter as well as a fast bomber and the Beaufighter was .... a fighter. The G4M was a medium bombers, not a small, fast bomber.

If you want to compare it with something, compare it to Whitleys, Wellingtons, Bostons, B-25s, and B-26s.

G4M: 266 mph. 1941. 2200 pounds bombs. 21000 pound airplane. 1770 mile range. 3130 mile ferry. Cruise 196 mph.
Whitley: 230 mph. 1937. 7000 pounds bombs. 33500 pounds airplane. 1650 mile range. 2400 mile ferry. Cruise 210 mph.
Wellington: 235 mph. 1938. 4500 pounds bombs. 28500 pound airplane. 2550 mile range. Cruise 195 mph.
Boston: 317 mph. 1941. 4000 pounds bombs. 24000 pound airplane. 945 mile range. 2300 mile ferry. Cruise 280 mph.
B-25: 272 mph. 1941. 3000 pounds bombs. 35000 pound airplane. 1350 mile range. Cruise 230 mph.
B-26: 278 mph. 1941. 4000 pounds bombs. 37000 pound airplane. 1150 mile range. 2850 mile ferry. Cruise 216 mph.

I seriously doubt any could haul the max bomb load and also go the max range. In any airplane, you trade payload for fuel.

So, as far as speed goes, the G4M is faster than a Whitely or a Wellington, about the same as a B-25 and the B-26 has a small speed advantage, but not enough to matter. NONE of them cruised at maximum speed, so I'm not sure why comparing maximum speeds is even relevant. The G4M cruised about like the bottom of the class, which wasn't all THAT much slower than the middle of the class. Only the B-25 and A-20 were significantly faster at cruise.

It serves to highlight the A-20, which is the fastest in the list and hauls a good payload.

The G4M doesn't seem to carry as much weight as the others, but it has a better standard range than all but the Wellington. They seem to have used it mostly as an attack airplane and not a medium bomber, going for specific tactical targets. All in all, the G4M is not especially impressive, but it also isn't too far behind the field if you are using it for tactical purposes. It is easily the lightest of the medium bombers above by a ton and a half.

One notes that it was the Whitley that was chosen for early bombing of Italy from UK bases.

 

[Shortround6]

My point is that the Allied planes were vulnerable too. The pilot armor also didn't always work, the rubber lined fuel tanks didn't always prevent fires. The Hurricane and Spitfire still had an unprotected (except for aluminum 'armor') fuel tank in front of the pilot as late as 1943.

Pilot armor and self sealing fuel tanks were good to have, but their importance is sometimes exaggerated. Read the operational histories. Zeros didn't burst into flames every time they were hit. Hurricanes and P-40s and P-39s were not immune to 20mm cannon fire. Their radiators did get punctured, yes sometimes by a single small caliber bullet, and that did result in planes going down. These are just facts.

Everything was a percentage.
Nothing worked 100% of the time.
Nothing failed 100% of the time.

Probability of kill goes through several stages.

Ph X Pd = Pk

Ph = probability of hit.
Pd = probability of damage.
Pk = probability of kill.

Both Ph and Pd have a number of components.

For Ph they can include (but not limited to)
number of rounds fired per engagement, this can be broken up several ways, like rounds per sec or rounds per burst or......
Pilot skill, accuracy of aim,,,which can depend on the sighting system used among others.
Range, which is flight time of projectiles.
target aspect
size of the target.
Speed of the target. like how much lead is needed and this goes back to range and target aspect.

Once you actually have hits on target we can discuss damage and this varies depending on the target aircraft in addition to the projectiles.
Most aircraft fired a mix of ammo. Most aircraft did NOT fire all the same types of ammo.
For the Germans with their 'mine' shells it was often about 40% (2 out of 5) mine shells in the drum or belt.
British often used 50/50 mix of HE and AP (or semi AP) for their 20mm guns.

For the importance of aiming and target aspect and rate of fire, in a hypothetical situation where a plane is flying 300mph at 90 degrees to a fixed gun that is firing at 600rpm the bullets will land 44ft apart on the aircraft, or 22ft apart from a gun firing at 1200rpm. At 45 degrees the bullets are closer together, if the gun traverses the hits can be much closer together.
The problem with combat reports is that tell you what happened but not why in regards to gunnery.
Range is unknown or guessed at or some something like "fired a burst at long range, closed the range and fired another burst, observed hits on fuselage " Which actually tells us nothing about the actual distances or wither pilot Bob and pilot Sam have the same meaning for long range and medium range. Also does not give any idea of rounds fired, 2 second burst or 3 second or 4 seconds. Most of the time the hits that are visible are tracers or incendiary (for the Germans 7.9mm explosive rounds) that give a visual indication. AP and ball don't give much of an indication which is why they used the indicator rounds. Problem is that at long range the indicatory rounds often don't hit where the non indicator rounds do.
It takes a lot of analysis of gun camera footage and ground testing to figure out what was happening. Like British figuring out that pilots were sometimes opening fire at 3 times the estimated distance. 900 yds instead of 300yds.

 

[PAT303]

300yds.

And even that is way too far, same with the idea that you aim for a certain part of the aircraft, the most vulnerable part, where's the radiator in this photo?.

 

[Wild_Bill_Kelso]

View attachment 727490
View attachment 727491View attachment 727495
Do you think the pilots of these Spitfires think pilot protection is overrated?.

No I don't, but for each one of those, there are multiple KiA and completely destroyed aircraft ripped apart by cannon shells. My point is that such protection only helped 'on the margins' - a good burst of 20mm or heavy machine gun, or even of the light machine gun and the plane was going down, often with a dead pilot.

 

[Wild_Bill_Kelso]

Everything was a percentage.
Nothing worked 100% of the time.
Nothing failed 100% of the time.

Probability of kill goes through several stages.

Ph X Pd = Pk

Ph = probability of hit.
Pd = probability of damage.
Pk = probability of kill.

Both Ph and Pd have a number of components.

For Ph they can include (but not limited to)
number of rounds fired per engagement, this can be broken up several ways, like rounds per sec or rounds per burst or......
Pilot skill, accuracy of aim,,,which can depend on the sighting system used among others.
Range, which is flight time of projectiles.
target aspect
size of the target.
Speed of the target. like how much lead is needed and this goes back to range and target aspect.

Once you actually have hits on target we can discuss damage and this varies depending on the target aircraft in addition to the projectiles.
Most aircraft fired a mix of ammo. Most aircraft did NOT fire all the same types of ammo.
For the Germans with their 'mine' shells it was often about 40% (2 out of 5) mine shells in the drum or belt.
British often used 50/50 mix of HE and AP (or semi AP) for their 20mm guns.

For the importance of aiming and target aspect and rate of fire, in a hypothetical situation where a plane is flying 300mph at 90 degrees to a fixed gun that is firing at 600rpm the bullets will land 44ft apart on the aircraft, or 22ft apart from a gun firing at 1200rpm. At 45 degrees the bullets are closer together, if the gun traverses the hits can be much closer together.
The problem with combat reports is that tell you what happened but not why in regards to gunnery.
Range is unknown or guessed at or some something like "fired a burst at long range, closed the range and fired another burst, observed hits on fuselage " Which actually tells us nothing about the actual distances or wither pilot Bob and pilot Sam have the same meaning for long range and medium range. Also does not give any idea of rounds fired, 2 second burst or 3 second or 4 seconds. Most of the time the hits that are visible are tracers or incendiary (for the Germans 7.9mm explosive rounds) that give a visual indication. AP and ball don't give much of an indication which is why they used the indicator rounds. Problem is that at long range the indicatory rounds often don't hit where the non indicator rounds do.
It takes a lot of analysis of gun camera footage and ground testing to figure out what was happening. Like British figuring out that pilots were sometimes opening fire at 3 times the estimated distance. 900 yds instead of 300yds.

Thanks for the primer on ballistics. I've shot machine guns on the range before.

I think the difficulties in hitting moving targets is why many pilots shot from closer than 300 yards. But we know that the British lost over 1,500 aircraft during the Battle of Britain, including more than 1000 fighters. So somebody was getting hit. And I think it is a safe bet that these were not all shot down by 7.92 mm machine guns, nor did the armor save everyone in those planes. The Germans lost even more of course (1887) though a smaller percentage of these were fighters (650 Bf 109 and 223 Bf 110).

The British lost 1500 pilots and aircrew during the BoB, including 544 fighter pilots. I'm sure some of them were saved by armor and SS tanks, but obviously that alone did not prevent dying in combat.

And of course, it is worth noting that both Hurricane and Spitfire were converted to cannon ammunition as quickly as possible in spite of the not trivial challenges, especially for the Spitfire. Right? Or did I miss something?

 

[Wild_Bill_Kelso]

I've read some rubbish in my time but this takes the cake, every country, EVERY country, even Japan fitted protection to their aircraft after the experienced and realisation of what an actually shooting war is like, often to the detriment of the aircraft's performance yet you think it's exaggerated?.

I salute your ability to write rubbish yourself mate

 

[GregP]

Thanks for the primer on ballistics. I've shot machine guns on the range before.

I think the difficulties in hitting moving targets is why many pilots shot from closer than 300 yards. But we know that the British lost over 1,500 aircraft during the Battle of Britain, including more than 1000 fighters. So somebody was getting hit. And I think it is a safe bet that these were not all shot down by 7.92 mm machine guns, nor did the armor save everyone in those planes. The Germans lost even more of course (1887) though a smaller percentage of these were fighters (650 Bf 109 and 223 Bf 110).

The British lost 1500 pilots and aircrew during the BoB, including 544 fighter pilots. I'm sure some of them were saved by armor and SS tanks, but obviously that alone did not prevent dying in combat.

And of course, it is worth noting that both Hurricane and Spitfire were converted to cannon ammunition as quickly as possible in spite of the not trivial challenges, especially for the Spitfire. Right? Or did I miss something?

None of the pilots they "lost" were saved. That's why they were called "lost." The ones who got shot down and survived are not listed as lost and that's why there is a difference between the number of planes shot down and the number pilots lost ... it's the guys who survived.

But, I'm pretty sure you know that.

 

[pbehn]

Thanks for the primer on ballistics. I've shot machine guns on the range before.

I think the difficulties in hitting moving targets is why many pilots shot from closer than 300 yards. But we know that the British lost over 1,500 aircraft during the Battle of Britain, including more than 1000 fighters. So somebody was getting hit. And I think it is a safe bet that these were not all shot down by 7.92 mm machine guns, nor did the armor save everyone in those planes. The Germans lost even more of course (1887) though a smaller percentage of these were fighters (650 Bf 109 and 223 Bf 110).

The British lost 1500 pilots and aircrew during the BoB, including 544 fighter pilots. I'm sure some of them were saved by armor and SS tanks, but obviously that alone did not prevent dying in combat.

And of course, it is worth noting that both Hurricane and Spitfire were converted to cannon ammunition as quickly as possible in spite of the not trivial challenges, especially for the Spitfire. Right? Or did I miss something?

Approximately half those shot down survived, but some were injured while many were not shot down but landed with injuries. Fitting of SS tanks and armour was an absolute requirement although you can read on this forum that the British just used it to get out of the P-39 contract. The Spitfire and Hurricane started carrying cannon in late 1940, what was th standard armament of a US P-40 in late 1940?

 

[Wild_Bill_Kelso]

Everything was a percentage.
Nothing worked 100% of the time.
Nothing failed 100% of the time.

Probability of kill goes through several stages.

Ph X Pd = Pk

Ph = probability of hit.
Pd = probability of damage.
Pk = probability of kill.

Both Ph and Pd have a number of components.

For Ph they can include (but not limited to)
number of rounds fired per engagement, this can be broken up several ways, like rounds per sec or rounds per burst or......
Pilot skill, accuracy of aim,,,which can depend on the sighting system used among others.
Range, which is flight time of projectiles.
target aspect
size of the target.
Speed of the target. like how much lead is needed and this goes back to range and target aspect.

Once you actually have hits on target we can discuss damage and this varies depending on the target aircraft in addition to the projectiles.
Most aircraft fired a mix of ammo. Most aircraft did NOT fire all the same types of ammo.
For the Germans with their 'mine' shells it was often about 40% (2 out of 5) mine shells in the drum or belt.
British often used 50/50 mix of HE and AP (or semi AP) for their 20mm guns.

For the importance of aiming and target aspect and rate of fire, in a hypothetical situation where a plane is flying 300mph at 90 degrees to a fixed gun that is firing at 600rpm the bullets will land 44ft apart on the aircraft, or 22ft apart from a gun firing at 1200rpm. At 45 degrees the bullets are closer together, if the gun traverses the hits can be much closer together.
The problem with combat reports is that tell you what happened but not why in regards to gunnery.
Range is unknown or guessed at or some something like "fired a burst at long range, closed the range and fired another burst, observed hits on fuselage " Which actually tells us nothing about the actual distances or wither pilot Bob and pilot Sam have the same meaning for long range and medium range. Also does not give any idea of rounds fired, 2 second burst or 3 second or 4 seconds. Most of the time the hits that are visible are tracers or incendiary (for the Germans 7.9mm explosive rounds) that give a visual indication. AP and ball don't give much of an indication which is why they used the indicator rounds. Problem is that at long range the indicatory rounds often don't hit where the non indicator rounds do.
It takes a lot of analysis of gun camera footage and ground testing to figure out what was happening. Like British figuring out that pilots were sometimes opening fire at 3 times the estimated distance. 900 yds instead of 300yds.

How many 20mm rounds do you figure it takes to blow the wing off of an airplane? one of the tailplanes? The verticle stabilizer and rudder?

This is from (I believe) a P-38 so it is a mix of 20mm and .50 cal hits, but look at the number of hits he is getting. More than 2-3 I would say, and the rounds are clearly not 44 ft apart. In fact i think there are about 20 hits from the flashes.


View: https://youtu.be/S3cpkQT4Njw?t=141

How many hits (again this is probably 'just' .50 cal) did it take to blow the wings off of these (presumably strongly built, armored) German planes


View: https://youtu.be/2pGz0FGLMCc?t=594

Like this one

View: https://youtu.be/2pGz0FGLMCc?t=613

 

[Wild_Bill_Kelso]

None of the pilots they "lost" were saved. That's why they were called "lost." The ones who got shot down and survived are not listed as lost and that's why there is a difference between the number of planes shot down and the number pilots lost ... it's the guys who survived.

But, I'm pretty sure you know that.

And I am pretty sure you are pouncing on clumsy grammar and pretending it's a claim I didn't make.

I'm referring to the difference between lost aircraft and lost pilots

 

[Wild_Bill_Kelso]

Approximately half those shot down survived, but some were injured while many were not shot down but landed with injuries. Fitting of SS tanks and armour was an absolute requirement although you can read on this forum that the British just used it to get out of the P-39 contract. The Spitfire and Hurricane started carrying cannon in late 1940, what was th standard armament of a US P-40 in late 1940?

For reasons I still don't understand, the US couldn't figure out how to make 20mm cannon work reliably, well into the 60s it seems. The US relied on machine guns, P-40 originally had a mix of 12.7 and 7.62 mm machine guns, later all 12.7mm. Pre-production versons had just two guns I think. As I'm sure you know.

My (I think obvious?) point is that the 20mm was quickly adopted by the British in spite of many problems and challenges, I'm sure in part influenced by their experiences in the BoB. And was at least part of standard fighter armament for every other nation in WW2 except maybe the Italians who came a little later to it.

I am sure the armor and ss tanks saved many lives, and I agree it's better to have them than not. I'm just pointing out that it wasn't a panacea. Neither was a parachute though that helped save lives too.

The British put their own pilots into Hawk-75 / 'Mohawks" in India to fight the Japanese, and it lacked ss tanks and barely had any armor. Right?

 

[Wild_Bill_Kelso]

One good question - would a P-40 or say, a Wldcat have been better with two 20mm cannon and maybe two 12.7mm guns? I think maybe yeah. Would the P-39 have been better with just a 20mm gun instead of the 37? Well, if you had a reliable 20mm gun then yes. We know that some of them did have 20mm guns in fact though in US service these had a variety of other problems (like the wrong fittings for oxygen etc.)

Apologies for mentioning the aircraft that shall not be named.

 

[BiffF15]

One good question - would a P-40 or say, a Wldcat have been better with two 20mm cannon and maybe two 12.7mm guns? I think maybe yeah. Would the P-39 have been better with just a 20mm gun instead of the 37? Well, if you had a reliable 20mm gun then yes. We know that some of them did have 20mm guns in fact though in US service these had a variety of other problems (like the wrong fittings for oxygen etc.)

Apologies for mentioning the aircraft that shall not be named.

You bring up a good point of why didn't we, in this case, utilize 20mm. I would personally rather have more rounds/ longer trigger time than much less rounds of higher efficacy. Also, it seems to me we had more fighter on fighter combat than fighter on bomber leading me to think that the old .50 was more than enough.

 

[Greg Boeser]

One good question - would a P-40 or say, a Wldcat have been better with two 20mm cannon and maybe two 12.7mm guns? I think maybe yeah. Would the P-39 have been better with just a 20mm gun instead of the 37? Well, if you had a reliable 20mm gun then yes. We know that some of them did have 20mm guns in fact though in US service these had a variety of other problems (like the wrong fittings for oxygen etc.)

Apologies for mentioning the aircraft that shall not be named.

You allude to the P-400, but there were also similar P-39D-1s. Pilots tended to prefer the 20mm over the 37mm, especially for air combat. It was more reliable, and the trajectory was closer to the .50 cals.

 

[BarnOwlLover]

Oddly, the XP-51F or G, if chosen as an interceptor, would likely have had 4x20mm cannons. Why the US couldn't get the HS404 to work until the AN/M3 and M24 (basically post war) is beyond me. The British fixed the problems with jamming (mostly due to not being entirely suited to wing mounting and weak primer strikes due to a poorly dimensioned chamber) fairly early on. They also developed a pretty compact belt feed system instead of using the Chatelleralt "drum" belt feed adapter, though that wasn't widely used until after the war.

IMO, give me a P-51 or F-82 with 4x20mm Hispano Mk Vs (which the AN/M3 and M24 were based on, though the M24 I've read did use electrically primed ammo) with 150+rpg, and I'd be happy.

 

[Wild_Bill_Kelso]

Let me clarify my position a little bit.

The Japanese fighter design philosophy in WW2 was that the best way to avoid being shot down was to outmaneuver our outrun your opponent, to stay above your opponent, and / or to attack where your opponent didn't have many fighters and you could outnumber them / achieve local numerical air superiority.

In 1940-41, the available aircraft engines were mostly in the 800-1200 hp range. Designers had a big challenge in adding all of the heavy things that it turned out actual warplanes needed - we don't think of radios as being heavy today but in 1940 they were quite heavy. The ART-13 radio weighed around 100 lbs. Pre war planes often had two or four machine guns. The British jumped this up to 8 guns. The Germans and Japanese added a pair of 20mm cannon. All the guns needed more ammunition than originally anticipated. All the planes needed more fuel than originally anticipated. Aircraft engines needed things like extra speed or double stage superchargers, which were heavier and took up more space.

Planes operating over the desert needed to carry things like water. Pilots needed parachutes. Planes operating over the sea needed to carry dinghys. Sometimes extra navigation gear like direction finders.

Armor and self sealing tanks added a lot more weight. Self sealing tanks also reduced the amount of space inside the tank for fuel. Significantly, like 20-30%.

So designers faced the challenge of either overloading a plane to the point that the engine couldn't carry it around the sky efficiently, or leaving out some crucial things to keep the performance where they wanted. As Sr6 and others often point out, F4F-3 was a fairly spry aircraft. F4F-4, with the extra pair of machine guns, protected tanks and folding wings was at a performance level which was barely adequate to the job. Nor did we figure this out overnight. Same with the early P-40s. P-40B was fairly 'spry', P-40C less so, P-40D and early P-40E were overloaded. And pilots died because of this.

Radial engines were (usually) lighter for roughly the same horsepower. Also (usually) a bit easier to maintain and a bit less vulnerable. All of this factored into the Japanese design decisions. It wasn't just that they were incapable of building strong things. Look at the Yamato for chrissakes.

You can't just absorb 20mm cannon shells
Or machine guns. When you read about a lot of earlier war Allied fighters and bombers, among the usual tropes you will often see a line like "it could take an enormous amount of punishment". Sure. They could. But this sometimes gets taken too far. I saw a recent youtube podcast about P-40s which claimed that the strategy used in North Africa was to let the Germans shoot them, absorb the damage due to armor and strong construction, and then counterattack. This is taking the idea of the ruggedness and armor to ridiculous extremes. A good burst from 20mm cannon shells will in most cases either destroy any fighter aircraft, or leave it crippled and limping for home. Even light machine guns would often do the same thing.

Pilots of Wildcats, P-40s, P-39s, Hurricanes and Spitfires avoided death and destruction by evading the enemy - outrunning, out turning, out diving or climbing. Disengaging and evading where the odds are against you. If they failed, the armor and ss tanks were there to save them. And sometimes did. What percentage of the time? I don't know, but nowhere near 50% I doubt even 25%. The armor will protect you from a few hits, but not a whole lot of hits.''

The Zero - neither invulnerable nor an easy mark
The A6M did suffer from a lack of armor and ss tanks. Clearly the Japanese recognized this because they did eventually add it to the Zero, and they had it on all their other fighers built after the Zero. Tactics like 'hit and run' and the Thach weave did work. But that doesn't mean they were easy. If you are fighting for your life and an enemy aircraft is shooting at you, the urge to turn to avoid the hits is not easy to resist. Speed differentials were not enough to evade without some separation. Many Japanese pilots, in A6M as well as the surprisingly lethal Ki-43, often did avoid being shot down by twisting, turning, and evading. Turning hard could save you from being hit. So could climbing above your opponent. And they did pull of lethal techniques like the Hineri Komi that only worked with such hypermaneuverable aircraft. They did hit where they weren't expected because of their (for the time) incredible range. Their guns did cause more damage, and this to a large extent did compensate for the armor on the Allied planes.

I would say in 1941 and early 1942, the A6M was an overall better balance of pros and cons than most Allied fighters and most German ones too. By the end of 1942 they were falling behind a little bit, and the big problem was that the replacement (A6M3) while better with almost twice the cannon ammunition and a two speed supercharger for better high altitude performance, was not enough of an improvement, and was worse in terms of range. What they needed at the end of 1942 was the A6M5 but that would take another year. I think this was their big flaw or failure, and you could say the Germans also failed in this regard to a large extent.

Allied pilots in the Pacific and China were not "losers".
Finally, I find it irritating that we often dismiss the overwhelming early Japanese victories because the crews out in this neck of the woods were somehow inferior. The RAF and RN / FAA may have sent some people they didn't like to the remote Theaters, and Australia and New Zealand were small countries. But the ANZACs proved to be some of the most effective fighters - on land and in the air - for the British Commonwealth in the Med. They weren't slacking close to home either. Milne Bay was one of the first real victories against the Japanese after they had beat down both British and American colonial forces, and that goes mainly to the Aussies.

The German pilots, too, faced somewhat unprepared opponents in the early years of WW2. But somehow they have a lot of people cheering with glazed eyed amazement all their victories over outnumbered Polish pilots in parasol wing, fixed undercarriage P.11s, outnumbered French pilots in planes they got a week before the war, Soviet peasant boys getting shot to pieces in their biplane during takeoff in some muddy field in Ukraine. And etc. Pick a position, but apply the same yard stick, I guess.

 

[Wild_Bill_Kelso]

You bring up a good point of why didn't we, in this case, utilize 20mm. I would personally rather have more rounds/ longer trigger time than much less rounds of higher efficacy. Also, it seems to me we had more fighter on fighter combat than fighter on bomber leading me to think that the old .50 was more than enough.

I think the point about fighter vs fighter is valid, certainly. If we had faced more problems from German bombers especially I think maybe we would have pushed harder to adapt the 20mm. But I do think a Wildcat with 20mm cannon with say, 120 rounds, might have been helpful in some of those 1942 naval battles.

Oddly, the XP-51F or G, if chosen as an interceptor, would likely have had 4x20mm cannons. Why the US couldn't get the HS404 to work until the AN/M3 and M24 (basically post war) is beyond me. The British fixed the problems with jamming (mostly due to not being entirely suited to wing mounting and weak primer strikes due to a poorly dimensioned chamber) fairly early on. They also developed a pretty compact belt feed system instead of using the Chatelleralt "drum" belt feed adapter, though that wasn't widely used until after the war.

IMO, give me a P-51 or F-82 with 4x20mm Hispano Mk Vs (which the AN/M3 and M24 were based on, though the M24 I've read did use electrically primed ammo) with 150+rpg, and I'd be happy.

Didn't the British put 20mm cannon in their Mustangs?