Spitfire Armaments

Suppose the production of the Hispano 20mm cannon ran into problems and/or its operational performance was way below what the RAF could accept, what would be done with the Spitfire's gun arrangements?

I assume that the universal wing, which could take 4 x 20mm cannon, 2 x 20mm + 4 x 0.303" or 8 x 0.303", could be adopted to take the Browning 0.50" HMG in the cannon bays.

But would they?

What other cannon options were available to the British around 1941/42?

If they did adopt the 0.50" HMG for the Spitfire, in what combinations would it be used?

4 x 0.50"
4 x 0.50" + 2 or 4 x 0.303"
2 X 0.50" + 4 x 0.303"

The elimination of the long barrels would have boosted performance by a small amount.

Until a two stage Merlin or any Griffon is available, use 4 .50s. After that, six should be used?

Other options, available in different years:
Copy the ShVAK (offer some money to the Finns for captured examples, or demand the blueprints and samples from the Soviets once the Germans attack them).
Copy the MG FF and/or MG-151.
Necked-up the .50 to produce a 15-18 mm cannon.
Copy the Breda SAFAT; having the guns in the wing solves the low synchronized RoF; neck it up to have a cannon.
Start talking with Oerlikon early enough.
Try fitting the ground-based Oerlikon in the wings, as maybe the worse of those options.

If the RAF had foreknowledge of irresolvable problems with the 20 mm Hispano, then the best option would have been licenced production of the FN 13.2x99 HMG.

This was a lightened version of the M2 Browinging (about 5 kg lighter) adopted for the fractionally larger and heavier 13.2x99 Hotchkiss round (otherwise identical to the 12.7x99) firing at 1000 rpm, at slightly reduced velocity (810-820 m/sec compared to 850-880 m/sec).

4 x 13.2 HMGs would have offered more power than eight .303s, at roughly the same weight.

tomo pauk said:

Until a two stage Merlin or any Griffon is available, use 4 .50s. After that, six should be used?

Other options, available in different years:
Copy the ShVAK (offer some money to the Finns for captured examples, or demand the blueprints and samples from the Soviets once the Germans attack them).
Copy the MG FF and/or MG-151.
Necked-up the .50 to produce a 15-18 mm cannon.
Copy the Breda SAFAT; having the guns in the wing solves the low synchronized RoF; neck it up to have a cannon.
Start talking with Oerlikon early enough.
Try fitting the ground-based Oerlikon in the wings, as maybe the worse of those options.

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Would 6 x 0.50" HMGs require a redesign of the Spitfire wing, or could the 0.50" fit in one of the outer 0.303" bays?

I seem to recall that early cannon fighter proposals suggested the Oerlikon. I was under the impression that the Oerlikon was passed over in favour of the Hispano, rather than it being late.

wuzak said:

Would 6 x 0.50" HMGs require a redesign of the Spitfire wing, or could the 0.50" fit in one of the outer 0.303" bays?

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I suspect they wouldn't fit in the 0.303 bays... but it's interesting because it raises the question, for me at least, if they would have even designed the universal C wing as they did if the RAF didn't have Hispanos to put in 'em.

tomo pauk said:

Other options, available in different years:
Copy the ShVAK (offer some money to the Finns for captured examples, or demand the blueprints and samples from the Soviets once the Germans attack them).

Click to expand...

Like many things, could take 1 to 2 years to get into production, especially if you have to reverse engineer it.

Copy the MG FF and/or MG-151.

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Two different situations as the MG FF (or it's equivalent) had been on the open market since the early 30s. British looked at the MG-151 and thought it took too much machining.

Necked-up the .50 to produce a 15-18 mm cannon.

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Perhaps but you get into diminishing returns very quickly as you go down in caliber for HE shells. Weight of projectile for similar shape varies with the cube of the diameter (roughly). An 18mm shell might only be 65% of the weight of 20mm (83 grams?) German 15mm HET weighed 57 grams compared to more 'normal' 120-130 grams for 20mm shells. Change type of projectile or shape and things can very considerably.
American .50 cal ammo has a base diameter of 20.3mm (diameter of case just in front of rim).
Russian 12.7mm ammo has a base diameter of 21.8mm.
Most straight 20mm rounds had base diameters of 21.8-22mm.
Most of the heavier 20mm shells had around 10 grams of HE
The German 15mm had 2.8 grams HE ( in part because it also had a tracer element)

Copy the Breda SAFAT; having the guns in the wing solves the low synchronized RoF; neck it up to have a cannon.

Click to expand...

This one isn't even close, the 12.7mm Breda SAFAT used a cartridge almost identical to the British .5in machine gun round. British have two much better options, use the .5 Vickers sort of as is, reliability being a bit of a problem or just scale the Browning action to use the .5 cartridge for a British version of the Japanese Ho-103 machine gun.



From Tony Williams excellent site.

The 12.7 x 81 case just isn't big enough to neck up to much.

Start talking with Oerlikon early enough.
Try fitting the ground-based Oerlikon in the wings, as maybe the worse of those options.

Click to expand...

The Oerlikon guns are not fast firing without a lot of work and may have more trouble converting to belt feed. The Japanese did mange both but it took a while.

Jabberwocky said:

If the RAF had foreknowledge of irresolvable problems with the 20 mm Hispano, then the best option would have been licenced production of the FN 13.2x99 HMG.

This was a lightened version of the M2 Browinging (about 5 kg lighter) adopted for the fractionally larger and heavier 13.2x99 Hotchkiss round (otherwise identical to the 12.7x99) firing at 1000 rpm, at slightly reduced velocity (810-820 m/sec compared to 850-880 m/sec).

4 x 13.2 HMGs would have offered more power than eight .303s, at roughly the same weight.

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Were FNs built anywhere outside of Belgium?

Swedish AF used 13,2mm HMG during the war, my bet is that they also produced it.

Good call on the Belgian HMG.

HBPencil said:

I suspect they wouldn't fit in the 0.303 bays... but it's interesting because it raises the question, for me at least, if they would have even designed the universal C wing as they did if the RAF didn't have Hispanos to put in 'em.

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IIRC, the mock-up installation of six Hispanos was tried on the Spitfire.

Shortround6 said:

Like many things, could take 1 to 2 years to get into production, especially if you have to reverse engineer it.

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Agreed.

Two different situations as the MG FF (or it's equivalent) had been on the open market since the early 30s. British looked at the MG-151 and thought it took too much machining.

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Agreed re. MG FF.
In case the RAF badly wants a cannon, but there are no Hispanos around (or anything cheaper), the machining would be applied to copy the MG-151. We can have Hurricanes with maybe only two 'MG-151' plus 4 Brownings etc.

Perhaps but you get into diminishing returns very quickly as you go down in caliber for HE shells. Weight of projectile for similar shape varies with the cube of the diameter (roughly). An 18mm shell might only be 65% of the weight of 20mm (83 grams?) German 15mm HET weighed 57 grams compared to more 'normal' 120-130 grams for 20mm shells. Change type of projectile or shape and things can very considerably.

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The 80-85 gram HE trumps the multiple .303 rounds. Having four of such cannons should at least equal the typical Spitfire battery (2 Hisso + 4 .303s). The cannon ammo load per barrel would be increased at least 50% from Spit's 120 rpg.

American .50 cal ammo has a base diameter of 20.3mm (diameter of case just in front of rim).
Russian 12.7mm ammo has a base diameter of 21.8mm.
Most straight 20mm rounds had base diameters of 21.8-22mm.
Most of the heavier 20mm shells had around 10 grams of HE
The German 15mm had 2.8 grams HE ( in part because it also had a tracer element)

Click to expand...

Thanks for the data.

This one isn't even close, the 12.7mm Breda SAFAT used a cartridge almost identical to the British .5in machine gun round. British have two much better options, use the .5 Vickers sort of as is, reliability being a bit of a problem or just scale the Browning action to use the .5 cartridge for a British version of the Japanese Ho-103 machine gun.
From Tony Williams excellent site.
The 12.7 x 81 case just isn't big enough to neck up to much.

Click to expand...

Agreed. Must admit that I've overlooked the .5 Vickers.

The Oerlikon guns are not fast firing without a lot of work and may have more trouble converting to belt feed. The Japanese did mange both but it took a while.

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It is again the case of whether RAF badly wants the cannon or not. The Oerlikon FF seem like decent weapon (Wikipedia; usual disclaimer applies):
The original "FF" used a slightly upgraded 128 gram 20x72mm round with a muzzle velocity of 600 m/s at a cyclic rate of 520 rounds per minute, almost double that of the original F and AF models.

The MV is a bit lacking, though.
The Ikaria MG FF was the German derivative? The Germans managed to come up with a 90-rd drum, such was used on the Fw-190. But I agree that a belt fed cannon is a better thing.

I found another potential cannon candidate - one that was considered for aircraft used by the Air Ministry, and considered for the Spitfire.

The Vickers 25.4mm cannon

The Spitfire connection
In "Spitfire, the History" by Morgan and Shacklady (Key Publishing Ltd, 1987) there is on page 61 a table of alternative armaments proposed for the Spitfire during its design/development phase. Included in these (rather surprisingly) is a 25.4mm Vickers. The data quoted for it match up almost exactly with the 25x189 gun and ammunition: a shell weight of .551 lbs (250 g); a muzzle velocity of 3,000 fps (914 m/s); a gun weight of 127 kg; and a length of 259 cm.

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double post

Rates of fire and projectile size have to be looked at. British .303, once they got production up, had an incendiary round with about 1 gram of material in it. With two guns delivering 40 rounds per second that is 40 grams per second of incendiary materiel for about 20-24 GK worth of guns and ammo at under 3kg per hundred.

Most countries seemed to get too tricky with .5in/12.7mm ammo and often had a variety of "multi-purpose" ammo which makes one wonder how good they were at any one thing. for example and again from Tony Williams excellent website



From left to right;
Ball with lead and aluminium filling.
API with incendiary filling (white phosphorous in the bullet tip).
APIT (Armor piercing incendiary tracer)
HEIT (High explosive incendiary tracer (?)

One can see a number of compromises and problems. Placing the incendiary compound in the bullet tip gives a good indication of bullet strikes and may work pretty good on fabric covered aircraft. It may not work so well on all metal aircraft as the incendiary compound gets stripped away on impact and does not penetrate very far into the aircraft. The triple threat APIT begins to show problems, the AP core is reduced in size and weigh resulting in less armor penetration. The incendiary compound in the nose is much reduced in size (good strike indicator?) to accommodate the tracer element in the rear although tracer element may contribute to incendiary effect inside aircraft. Round #4 shows a few more problems, one is that decent fuses can only be made so small and take up a disproportionate amount of room inside small projectiles. 2nd is that trying to combine HE rounds with tracer cuts into the HE capacity rather severely. Round #4 is carrying 0.8 grams of Penthrite wax.

Ammo weight has gone up to around 10.7kg per hundred in links. American .50 cal can weigh 13.9kg in links.

Slow firing 20mm cannon pack a punch when the shell lands but they weigh over twice as much as a .303 gun (even for a very light 20mm) and the drums are not light either. One 20mm gun listed weights of empty drums as 9kg for a 45 round, 10 kg for a 60 round, 12kg for a 75 round and 13kg for 100 round, ammo was 240 grams per round.

A big part of this question is when? Summer of 1940 and the Hispano proves to be crap and the British are scrambling not only for the Spitfire but for ALL their future fighters? 1938 when they still have time to do something?

Madsen made 20mm and 23mm guns for aircraft use. There is also the BESA 15mm. I know nothing about rates of fire or weight maybe someone has the figures.

Good post, SR6.

There might not be much of a reason for the ~30g projectile to mess around with a complicated and expensive fuzes, indeed. Hence my proposal for necking out HMG cartridges, so a more worthwhile HE content might be carried.

Slow firing 20mm cannon pack a punch when the shell lands but they weigh over twice as much as a .303 gun (even for a very light 20mm) and the drums are not light either. One 20mm gun listed weights of empty drums as 9kg for a 45 round, 10 kg for a 60 round, 12kg for a 75 round and 13kg for 100 round, ammo was 240 grams per round.

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All fine; the 20mm ammo weighting 240 g is for the 'hi-power' suff, like Hispano. The MG-FFM was at ~180g ('regular' shell) or at ~160g (mine shell - maybe the Allies might adopt that, too?). The MG-151/20 was at 180g (mine shell) and 202 g ('regular' shell). The necked-out cartridge (17-18 mm) weight should be in the ball park with MG-FFM with mine shell. Not as destructive, but having four such canons should more than make up for that.

A big part of this question is when? Summer of 1940 and the Hispano proves to be crap and the British are scrambling not only for the Spitfire but for ALL their future fighters? 1938 when they still have time to do something?

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Not sure - whether it is the original Hispano, or British Hispano, that enters into problems and/or RAF is not satisfied with:

Suppose the production of the Hispano 20mm cannon ran into problems and/or its operational performance was way below what the RAF could accept, what would be done with the Spitfire's gun arrangements?

Wuzak?

BTW: this seems like a good reading: http://www.ibiblio.org/hyperwar/USN/ref/MG/index.html

Shortround6 said:

A big part of this question is when? Summer of 1940 and the Hispano proves to be crap and the British are scrambling not only for the Spitfire but for ALL their future fighters? 1938 when they still have time to do something?

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My original premise was that the Hispano made it into production and into the Spitfiree, such that the universal wing has been designed, when it is discovered that it isn't working as required (ie it is crap). So, basically, late 1940.

I would think that the problems with the Hispano would be solved - eventually. But, in the mean time, the British have to find alternatives - and quickly.

British are pretty much stuck then. Perhaps they can get a few thousand .50s from the US but with no production line set up any of the foreign cannon or MG alternatives are many months (or years) away from service use. Even trying to adapt the .5 Vickers gun could take several months and perhaps not be very successful in the end.

Stick in the eight .303s and make all the incendiary ammunition you can.

BTW, the Hurricane II and Typhoon are stuck with twelve .303s and the Beaufighter and Whirlwind are armed ????????

There was a 12-Browning installation built and tested by Martin Baker for the Whirlwind in case the Hispano didn't pan out.

I like the idea of putting the 15mm BESA into the frame as a stand by. It was automatic, belt fed, in production and designed as an anti tank gun so power and penetration shouldn't be a problem but had a slow ROF 430 rpm. If you could work on the ROF it has some potential

BESA 15mm wasn't a success asan automatic AFV cannon/HMG, in automatic fire the barrel vibrated and so ruined the accuracy so it was mainly used as a single shot weapon. So at least as turret weapon it was a lousy automatic gun.

Juha

Juha said:

BESA 15mm wasn't a success asan automatic AFV cannon/HMG, in automatic fire the barrel vibrated and so ruined the accuracy so it was mainly used as a single shot weapon. So at least as turret weapon it was a lousy automatic gun.

Juha

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The 7.92 BESA was noted for its accuracy so there is nothing fundamentally wrong with the gun, the barrel looks very long so maybe it isnt supported properly. Vickers produced for trials purposes a HMG version of the Vickers K .303 in 13.2x99 the Vickers K was very reliable so maybe that was an option if it is built in 12.7x87.

All these options need the RAF to have 20/20 foresight as building a production line takes a long time I would say at the very least a HMG or Cannon replacement for the Hispano needs to be started in 1938 and even then it probably wouldnt be ready any earlier than a Hispano.