Guns & Cannon: Rules of Thumb

[Zipper730]

I'm curious if there's a generalized metric when it comes to guns and cannon (allies at least)? I've generally seen figures similar to this

• 8 x 0.303, or...
• 6 x 0.50, or...
• 4 x 20mm, or...
• 2-3 x 30mm, or...
• 2 x 37mm/40mm...

It's clearly not perfect but the idea sort of came out of observations, as well as discussion with others.

• Hawker Hurricane (1935/11/6)
  • Designed with 8 x 0.303 to allow it to deliver enough bullets onto a bomber in 2-seconds
  • Later variants were developed with 4 x 20mm cannon
  • There was one variant built that had 2 x 40mm cannon
  • Exceptions: There was a variant built that had 12 x 0.303 and no cannon equivalent with 6 x 20mm
• Supermarine Spitfire (1936/3/5)
  • Designed with 8 x 0.303 for the same reason as the Hurricane
  • Proposals were made at some point for 6 x 0.50, and even something like 2 x 30-40mm cannon
  • Variants were built that carried 8 x 0.303, 2 x 20mm + 4 x 0.303; 4 x 20mm
    • Exceptions: The predecessors to the B-wing had only 2 x 20mm instead of 4 x 20mm, and the final set-ups had provision for 2 x 20mm + 2 x 0.50
• Bell P-39 (1938/4)
  • The P-39D had 4 x 0.303 in the outer wings, later replaced on some models with 2 x 0.50
• Vought F4U
  • 6 x 0.50 operational variants except one or two that had 4 x 20mm
• Bell YP-59 (1942/10/1)
  • One set-up had 1 x 37mm + 3 x 0.50; another had 2 x 37mm
• Grumman XP-65/F7F (1943/11)
  • The USAAF proposal had 2 x 37mm + 4 x 0.50; the USN had 4 x 20mm + 4 x 0.50
    • The USAAF version was not built
• North American F-86 & Derivatives
  • Baseline F-86: 6 x 0.50
  • FJ-2/-3/-4: 4 x 20mm
  • F-86F Gunval: 4 x 20mm

It wasn't absolutely perfect as the Typhoon had 12 x 0.303 replaced with 4 x 20mm not 6 x 20mm.

 

[fubar57]

The Hurricane Mk.IID, besides the 40mm cannon also had two mgs used for aiming

 

[parsifal]

armament actually developed over time. the hurricane and spitfires were initially designed with 4 guns. I am pretty sure the Belgian and Yugoslav hurricanes were both the 4 gun variant.

Early US fighters were generally fitted with 1 x 0.30 cal and 1 x 0.50 cal mgs. This was increased to 2 x 0.50 cal from about 1940. Early Grumman f4fs (F4f2) had only two MGs the early Grumman F4f3 were equipped with 4 x 0.5 MG. Only after combat experience provided by the RN martlet sqns was the a/c firepower increased to 6 x 0.5 MG, and then only with a significant weight penalty and a reduction in the RPG. Many USN flyers disliked the F4F4 because of that.

Italian and Japanese a/c were generally only fitted with 2 x 7.7mm MG until 1940, after which there was a steady increase in firepower. these aircrafts with small HP engines struggled to lift the broadside they carried.

Soviets and French aircraft tended to favour 1 x 20mm and 2x 12.7mm MG

 

[billrunnels]

The Hurricane Mk.IID, besides the 40mm cannon also had two mgs used for aiming

How were they used for aiming?

 

[parsifal]

How were they used for aiming?

bill ive read they were used for sighting.....the pilot would use them to find a line along the ground....as the bullets threw up dirt and debris, it could be estimated when to fire those huge 40mm shells. The recoil of these guns was so bad they could tear the wings off the aircraft ive read so it was advisable not to fire off too many rounds if possible. .

 

[Greyman]

I think the whole '.303s to aim the 40mm' thing with the Hurricane IId for the most part isn't true, and once it made it into a book it just kept getting repeated. As for tearing the wings off, I don't think the physics allows for that whatsoever and it certainly wasn't an issue. Same with tall tales of the aircraft performing snap-rolls when one gun jammed.

I have a number of primary sources on the Hurricane IId (reports/training syllabuses/etc.) and they are very specific about how the 40mm guns are aimed - very deliberately through the use of the GM2 gunsight at a specific speed.

Later in training (and ultimately in combat, of course) the machine guns were fired throughout the attack run in order for the incendiary ammunition to ignite any exposed/flowing flammable material.

Other considerations:

• The guns and sight were harmonised for 500 yards and 240 mph right on the deck. Fire was to be opened at 700 yards. I haven't crunched any numbers but I have a feeling the trajectories of the two weapon types wouldn't allow for precision aiming with the .303-in guns.
• The group size of a .303 Browning in a Hurricane wing is about four times the size of that from a 40mm Vickers 'S' gun.

Now, of course I'm fully prepared to be contradicted by an anecdote or two - especially from the Hurricane units operating in the Far East - but everything I've read from official sources of the time indicate the cannons were aimed with just the gunsight.

 

[billrunnels]

bill ive read they were used for sighting.....the pilot would use them to find a line along the ground....as the bullets threw up dirt and debris, it could be estimated when to fire those huge 40mm shells. The recoil of these guns was so bad they could tear the wings off the aircraft ive read so it was advisable not to fire off too many rounds if possible. .

Thanks for the reply. Interesting concept of aiming.

 

[Ivan1GFP]

How were they used for aiming?

Hello BillRunnels,
Probably by sighting in with MG fire and then fire for effect with cannons when MG strikes can be observed.

Hello Parsifal,
As you stated, the 6 gun armament of the F4F-4 was not so well thought of. I have seen it described as an attempt to have common armament with the Martlet / Wildcat versions being built for the Royal Navy who insisted on a 6 gun armament.
This can be seen by later variants of the Wildcat.
The FM-1 (F4F-4 equivalent) built by General Motors reverted back to the 4 gun armament as on the F4F-3.
The follow-on FM-2 (F4F-8) also used only a 4 gun armament.

The Russians were an interesting bunch. Their late war Yak fighters typically only mounted a motor cannon and a single cowl machine gun.
They could get away with it because they achieved extremely high firing rates for most of their machine guns.
They didn't really like wing armament and often removed it from lend lease fighters.

Hello Zipper730,
The Spitfire could never have mounted 6 x .50 cals. There simply was not the room without a serious redesign of the wing planform.
The chord outboard of the cannon bays was too short to mount ..50 cals which is why they were mounted in the inboard cannon bays.

- Ivan.

 

[billrunnels]

I think the whole '.303s to aim the 40mm' thing with the Hurricane IId for the most part isn't true, and once it made it into a book it just kept getting repeated. As for tearing the wings off, I don't think the physics allows for that whatsoever and it certainly wasn't an issue. Same with tall tales of the aircraft performing snap-rolls when one gun jammed.

I have a number of primary sources on the Hurricane IId (reports/training syllabuses/etc.) and they are very specific about how the 40mm guns are aimed - very deliberately through the use of the GM2 gunsight at a specific speed.

Later in training (and ultimately in combat, of course) the machine guns were fired throughout the attack run in order for the incendiary ammunition to ignite any exposed/flowing flammable material.

Other considerations:

• The guns and sight were harmonised for 500 yards and 240 mph right on the deck. Fire was to be opened at 700 yards. I haven't crunched any numbers but I have a feeling the trajectories of the two weapon types wouldn't allow for precision aiming with the .303-in guns.
• The group size of a .303 Browning in a Hurricane wing is about four times the size of that from a 40mm Vickers 'S' gun.

Now, of course I'm fully prepared to be contradicted by an anecdote or two - especially from the Hurricane units operating in the Far East - but everything I've read from official sources of the time indicate the cannons were aimed with just the gunsight.

Thanks for the reply.

 

[Shortround6]

I'm curious if there's a generalized metric when it comes to guns and cannon (allies at least)? I've generally seen figures similar to this

• 8 x 0.303, or...
• 6 x 0.50, or...
• 4 x 20mm, or...
• 2-3 x 30mm, or...
• 2 x 37mm/40mm...

It's clearly not perfect but the idea sort of came out of observations, as well as discussion with others.

• Hawker Hurricane (1935/11/6)
  • Designed with 8 x 0.303 to allow it to deliver enough bullets onto a bomber in 2-seconds
  • Later variants were developed with 4 x 20mm cannon
  • There was one variant built that had 2 x 40mm cannon
  • Exceptions: There was a variant built that had 12 x 0.303 and no cannon equivalent with 6 x 20mm
• Supermarine Spitfire (1936/3/5)
  • Designed with 8 x 0.303 for the same reason as the Hurricane
  • Proposals were made at some point for 6 x 0.50, and even something like 2 x 30-40mm cannon
  • Variants were built that carried 8 x 0.303, 2 x 20mm + 4 x 0.303; 4 x 20mm
    • Exceptions: The predecessors to the B-wing had only 2 x 20mm instead of 4 x 20mm, and the final set-ups had provision for 2 x 20mm + 2 x 0.50
• Bell P-39 (1938/4)
  • The P-39D had 4 x 0.303 in the outer wings, later replaced on some models with 2 x 0.50
• Vought F4U
  • 6 x 0.50 operational variants except one or two that had 4 x 20mm
• Bell YP-59 (1942/10/1)
  • One set-up had 1 x 37mm + 3 x 0.50; another had 2 x 37mm
• Grumman XP-65/F7F (1943/11)
  • The USAAF proposal had 2 x 37mm + 4 x 0.50; the USN had 4 x 20mm + 4 x 0.50
    • The USAAF version was not built
• North American F-86 & Derivatives
  • Baseline F-86: 6 x 0.50
  • FJ-2/-3/-4: 4 x 20mm
  • F-86F Gunval: 4 x 20mm

It wasn't absolutely perfect as the Typhoon had 12 x 0.303 replaced with 4 x 20mm not 6 x 20mm.

The "metric" leaves out a lot. Like may of the later planes got much more powerful engines which enables a much heavier weight of guns and ammo to be carried.
Hurricane went from an 880 hp engine at take-off (and it's fixed pitch prop only allowed a fraction of that power to be used) to an engine rated at 1280hp for take-off (without using a combat rating) and a constant speed propeller. This allowed for the carriage of a heavier, higher drag armament at somewhat higher performance.

Gun production has to be taken into account. Not how many guns you might desire in an airplane but how many guns per month are coming out of the factories to be divided up between how many airplanes. In some cases large numbers of machine guns were used until cannon production could be increased to meet the demand, not because they really thought that 12 machine guns was really that good.

Changes in ammunition and guns also make nonsense of some simple comparisons. The six .50 cal guns in an F-86 had a combined firing rate of about 9 late WW II .50 cal guns. They also used different ammo. It much higher velocity making defection shooting easier and the ammo carried a much, much larger incendiary charge making hits much more likely to set the target on fire.

The Navy Furies also used a different 20mm cannon than WW II or immediately post war aircraft used. A highly modified Hispano that could fire at 1000rpm and using a cartridge NOT interchangeable with any other 20mm cannon. Reliability was a bit suspect.

Air Force cannon armed F-86 Sabres in Korea were fitted with trial versions of what would become the M-39 cannon. A revolver cannon of 1500rpm rate of fire.
This makes total nonsense of trying to compare them to WW II aircraft or even 1946-49 aircraft.

 

[buffnut453]

Same with tall tales of the aircraft performing snap-rolls when one gun jammed.

The 40mm cannon on the Hurri MkIID were actually configured to fire alternately rather than both at the same time, presumably to reduce the impact of recoil.

Here's a cool vid showing it in action:

 

[Timppa]

Early US fighters were generally fitted with 1 x 0.30 cal and 1 x 0.50 cal mgs.

For example, B-239 was armed from the start with 3x50 cal and 1x0.30 cal. Most 75 Hawks were also more heavily armed.

Italian and Japanese a/c were generally only fitted with 2 x 7.7mm MG until 1940

Standard armament of Fiat G.50 in 1939 was two 12.7mm Breda-Safat from the start.

Soviets and French aircraft tended to favour 1 x 20mm and 2x 12.7mm MG

AFAIK French aircraft did not use 12.7mm guns. It was the 7.5mm MAC 1934 possibly combined with (rather unreliable) HS 404 20mm cannon.
Typical Soviet fighters in 1939, I-153 and I-16 carried 4 fast firing 7.62 mm ShKAS . 12.7mm Berezin appeared later than 20mm ShVAK . Some I-16 versions (starting from Type 12 in 1936) had 2x20mm and 2xShKAS.

 

[Shortround6]

The P-26,P-30, P-35 and P-36 (at least the the majority) carried two guns in the cowl/fuselage. one was always a .30 cal. On the first two aircraft there was an option to replace the 2nd .30 cal with .50 cal. On the last two aircraft to was almost always one .30 and one .50. Last batch of P-36s (the C) added a .30 in each wing. one off prototypes differed and export planes differed.
The Navy Grumman F3F biplanes carried one of each, mostly. On occasion there might have been a a plane with two .30s.

The Italians were all over the place. twin 12.7s date back to many of the CR 32 biplanes let alone the CR 42. However not all aircraft of each type carried one or the other. Ground attack versions often had an extra pair of guns under the wings.

French, as has already been stated, used no 12.7mm (or 13mm/13.2mm) machine guns in service aircraft.
20mm usage was mixed, with older aircraft using HS 7s or HS 9s ( licensed Oerlikons) with much lower rates of fire than the HS 404.
I have no idea if the HS 404 could be refitted to aircraft built with HS 9s.

 

[tomo pauk]

armament actually developed over time. the hurricane and spitfires were initially designed with 4 guns. I am pretty sure the Belgian and Yugoslav hurricanes were both the 4 gun variant.

Early US fighters were generally fitted with 1 x 0.30 cal and 1 x 0.50 cal mgs. This was increased to 2 x 0.50 cal from about 1940. Early Grumman f4fs (F4f2) had only two MGs the early Grumman F4f3 were equipped with 4 x 0.5 MG. Only after combat experience provided by the RN martlet sqns was the a/c firepower increased to 6 x 0.5 MG, and then only with a significant weight penalty and a reduction in the RPG. Many USN flyers disliked the F4F4 because of that.

Italian and Japanese a/c were generally only fitted with 2 x 7.7mm MG until 1940, after which there was a steady increase in firepower. these aircrafts with small HP engines struggled to lift the broadside they carried.

Hurricane was designed with 8 LMGs, both Belgian and Yugoslav Hurricanes carried 8 LMGs. SPitfire's 1st armament actually installed was also 8 LMGs, despite early proposals for just 4.
F4F2 was just a prototype.

...
The Russians were an interesting bunch. Their late war Yak fighters typically only mounted a motor cannon and a single cowl machine gun.
They could get away with it because they achieved extremely high firing rates for most of their machine guns.
They didn't really like wing armament and often removed it from lend lease fighters.

The rate of fire of the Beresin HMG was high, but not that high. Granted, Skash LMG fired very fast. Light armament of the Yaks, and not just them, was not a feature, but a bug - they never faced hordes of heavy bombers flying above 7 km, so the outdated M-105 line of engines were flying mostly at their best altitude, and 20mm was in position to make a hard kill or a mission kill.
There was a reason why Soviets produced and used a number of fighters armed with 37mm cannon.

Hello Zipper730,
The Spitfire could never have mounted 6 x .50 cals. There simply was not the room without a serious redesign of the wing planform.
The chord outboard of the cannon bays was too short to mount ..50 cals which is why they were mounted in the inboard cannon bays.

There was a mock up of Spitfire with 6 (six) cannons, so certainly 6 .50 cals could've been carried. There was also a model with 4 cannons ad 4 LMGs produced in penny packets.

 

[Ivan1GFP]

Hello Tomo Pauk,

The Message alerts do not seem to be working well. The alert for this post came in just a couple minutes ago after I had missed your reply.

The rate of fire of the Beresin HMG was high, but not that high. Granted, Skash LMG fired very fast. Light armament of the Yaks, and not just them, was not a feature, but a bug - they never faced hordes of heavy bombers flying above 7 km, so the outdated M-105 line of engines were flying mostly at their best altitude, and 20mm was in position to make a hard kill or a mission kill.
There was a reason why Soviets produced and used a number of fighters armed with 37mm cannon.

Agreed regarding the Russians never having to intercept heavy bombers.
Which Russian fighters used a 37 mm cannon?

There was a mock up of Spitfire with 6 (six) cannons, so certainly 6 .50 cals could've been carried. There was also a model with 4 cannons ad 4 LMGs produced in penny packets.

I know there is space to mount 4 heavy guns and 4 light machine guns inside the Spitfire wing but apparently this would result in a weight problem.
I am very curious about the 6 cannon Spitfire and will have to look for it because I just don't see where the extra pair of cannon would go.
They can't go inboard because the main landing gear gets in the way.
The wing is thin and chord is short to mount them outboard without a lot of stuff sticking out or in bulges.

- Ivan.

 

[tomo pauk]

...
Agreed regarding the Russians never having to intercept heavy bombers.
Which Russian fighters used a 37 mm cannon?

Operatively - Yak-9K and LaGG-3-37. 37 mm was also tested aboard the Yak-3 and IIRC Yak-7. Soviets also tested the 45mm automatic cannon aboard the Yak-9, the recoil was too strong and that set-up was abandoned.

I know there is space to mount 4 heavy guns and 4 light machine guns inside the Spitfire wing but apparently this would result in a weight problem.
I am very curious about the 6 cannon Spitfire and will have to look for it because I just don't see where the extra pair of cannon would go.
They can't go inboard because the main landing gear gets in the way.
The wing is thin and chord is short to mount them outboard without a lot of stuff sticking out or in bulges.

- Ivan.

Spitfire's chord was long, even aboard the historical outer cannon place.

 

[Greyman]

Hurricane was designed with 8 LMGs, both Belgian and Yugoslav Hurricanes carried 8 LMGs.

During early planning/manufacture the Hurricane prototype had two Vickers guns in the fuselage and one in each wing.

The Belgians had a version with four 13.2mm Brownings - but only two were completed before the invasion ... and I'm not sure if these were able to get into action.

 

[Greyman]

The 40mm cannon on the Hurri MkIID were actually configured to fire alternately rather than both at the same time, presumably to reduce the impact of recoil.

I've never heard of this - and in fact have read mountains of evidence to the contrary.

 

[fastmongrel]

Griffon engined MkXII with a six cannon installation. It was actualy just a trial to see if six guns had any effect on flight handling I dont think they were ever fired and might just have been dummy barrels and ballast.

 

[Shortround6]

I am not sure if that was a "real" MK XII or a Prototype of what became the MK XII. I do believe it was a dummy installation.