Italian lack of an indigenous 20mm cannon

[greybeard]

Hi all,

I read very interesting CharlesBronson's article about italian aerial weapons, but an explanation is missing about development of an italian 20 mm or similar kind of automatic cannon.

I wonder if there's some "official" reason or reliable study about this.

GB

 

[CharlesBronson]

Because you cannot get this.....

Isotta Fraschini Scotti 20mm

or this....

Breda 35 20mm

...into a Macchi.

 

[tomo pauk]

It may depend on what kind of Macchi? If you really want to stick those heavy hitters in an existing fighter, the easiest way is to bury them (if partially only) in a wing, or mount them in an under-wing gondola. But if such a configuration is powered with just 840 HP (as in MC.200), we have just built an under-performer - due to the increased weight drag of that kind of a plane. If that's MC.202, such a configuration makes more sense.
The other thing is that Italians are lacking an indigenous V-12 that can enable an engine-mounted cannon. By the time such an engine 'arrives', in reality a licensed product in 1941, it's a better bet to produce MG-151/20 (or use such German cannons).

Perhaps Italians were wrong to 'insist' that their favored fighter engine is to be of radial type (= in reality an offspring of foreign design), 'stead of going for a HS-12Y from mid 30's on?

 

[CharlesBronson]

The performance of a mc 200 or Mc 202 with underwing 20 Scottti or Breda 35 guns ( wich arent belt feed so they woudl need a drum or some sort of magazine) woulndt be particulary brilliant. I think also there was a overconfidence in the effectivenes of the 12.7mm High explosive ammunition, yes the Breda Safat .50 was a good weapon, but explosive bullet in that caliber is ridiculous, even with today technology.

 

[greybeard]

Thanks for your comments and for posting those two 20 mm whose existance I didn't know.

I was wondering if historical reasons would have ever issued (like famous Mussolini's one about lack of aircraft carriers in italian Navy) or a study based on historical documents. I know that's hard, also because political rule of that era wasn't obviously open minded.

Performance of a 20 mm cannon-armed italian fighter I think would have been comparable with contemporaries like M.S. 406 or Mitsubishi Zero; seemingly, Italy did a different choice (probably to keep confidence with .50 Breda-S.A.F.A.T. - since still in 1970's there were veterans still claiming effectiveness of the twin guns arrangement), never stated anywhere.

 

[CharlesBronson]

No problem caro "Barbagrigia", the italians bought the Oelikon L, a medium size variant of the 20mm swiss cannon family for the use in some pre-war flying boat like the Savoia s62, however they didnt apply those in any fighter, probably because they havent V12 engined fighters at the time (1934-38 ) to place them between the cilinder banks.

Italy did a different choice (probably to keep confidence with .50 Breda-S.A.F.A.T. - since still in 1970's there were veterans still claiming effectiveness of the twin guns arrangement), never stated anywhe

It had some advantages, is more easy to aim and less need to harmonization with the reflex gunsight compared with wing guns, the rate of fire, that is usually a weakness of this type of emplacement, the Bredas 12.7mm fired 700 rpm in free mounting and 470-500 in synchronous mode so you can see the differences.

 

[vikingBerserker]

As always, great info CB!

 

[Dogwalker]

A little late to join the party, but the theme is interesting...
Sorry for my bad english, there are several years I do not write in english so much.

in reality, Italy pionereed the use aerial auto cannons, with the 25mm Fiat-Revelli gun (magazine fed, eight round), about 200 of which were installed, during WWI, in the Macchi flying boats. The weapon proved to be reliable, and light enough to be installed in flexible mountings, but was unfavoured by the crews cause, using HE rounds, if, for every reason, the action would cycle without having correctly extracted the last case, the result would be deadly for the gunner (later, both the tray-fed Breda 20/65 and Scotti 20/77 had an internal safety to prevent that).
An eventual development, done by replacing the big and slow 25mm projectile with a smaller and faster 20mm one, in the same 87mm case, and feeding it with a drum magazine, would have resulted in a rough equivalent of the MGFF. But in the '30s Fiat was no more producing firearms, and probably almost nobody remembered the weapon.

There are several reasons to the italian failure of developing a 20mm aerial cannon prior to the war, but, the first one, was surely the time factor.
That's difficult to understand today, when 20 years old fighter are still good for first-line service, but, in a 5 years span only, in the second half of the '30s (moreover, a period of economic crisis), aero fighters developed from biplanes armed with a pair of rifle-calibre MGs, to metallic monoplanes armed with eight MGs, three cannons, and so on.
In this scenery, the nations that recognized first than the others the necessity of improving the firepower of their planes, risked to be outgunned by the last ditch efforts made by the others, literally few days before the outbreak of the war.
That's the present case. Italy was one of the first powers in recognising the necessity of replacing the rifle-calibre MGs with heavier weapons. The studies for the 12.7mm Breda-SAFAT begun at the end of '20s, the weapon was ready in the early '30s, experimentally installed in some Fiat CR30, and standard in Fiat CR32 (first flew in 1933, in line in 1935).
Equipped with them, for example, the pilots of CR.32s (a fighter they already know would soon be replaced, and it was only two years old) that witnessed the brand new Bf109 B1, B2 and C in action in Spain 1937-38, could hardly have been impressed by their armament of two, three (whit the often-jammed third MG of the Bf109b2 making bad press to propeller-hub-firing weapons also) and four rifle-calibre MGs respectively (and also by their 640hp Junkers Jumo 210 engine for that matter).
In the end, still in 1938, a pilot armed with a pair of heavy machine guns, could think to be very well armed compared to its opponents (and the competition to choose the monoplane fighter of the Regia was launched in 1937). A year later, with the same armament (and a much more powerful engine) he was outgunned (and outengined).
We can see the same problem whit the other power that choose to rely on heavy MGs.
In 1936 the Grumman F3F entered in line armed wit a 0.30 and a 0.50 Browning. In 1937 the P-35 had two 0.30 and two 0.50. So was armed the P-40 until the D Version (and, at that point, the war in Europe had already begun). Better than the Breda SAFAT couple, but not an impressive armament at all. But the U.S. entered the war later, and had the time, and the manufacturing capability, to use the European lesson.

The second part of the equation is the different role of the weapon manufacturers, the aircraft manufacturers, and the government.
The Breda firm helped producing the Fiat-Revelli MG during WWI, but, in the mid '20s, decided to enter in the MG market with autonomous projects, in competition with the Fiat ones. It's first products were a series of recoil operated weapon, using the patented Mascarucci breechlock (ironically, the same development led to the highly humoral Breda-30 and the stone-axe reliable Breda-SAFAT) whose ultimate development, the will-be Breda SAFAT, won the competition with the Fiat concurrent product and the subsequent lawsuit brought by Fiat itself. As a result Fiat decided to leave the firearms market, selling his specialized subsidiary SAFAT to the Breda itself.
At that point Breda was pratically a monopolist in the Italian heavy MG market, since the only Italian competitor, the "Autoscotti" was not really a manufacturer, but a single inventor, Alfredo Scotti, who sold the projects of the weapons he designed, (all, from the "Scotti model X" rifle, to the "Cannone Mitragliera 20/70", based on the same gas-unlocked-blowback mechanism he patented in 1928 ), to other firms, as the Swiss Oerlikon, or the Isotta Fraschini.
But, this did not slow the inventiveness of Breda technicians. In 1929 the firm acquired the licence to produce the gas operated Hotchkiss 13.2mm MG (after two years of development, that became the Breda-31, adopted by the navy), and then, having developed a gas operated mechanism of his own (single lug, rising bolt due to the inclined surfaces in the bolt carrier), produced a series of gas operated weapons (6.5mm-8mm Breda-PG battle rifle, 8mm Breda-37 and Breda-38 MGs, 20mm Breda-20/65 and 37mm Breda-37/54, all introduced from 1934 to 1938, quite a result for a brand that had first experienced gas operated MGs only on the Hotchkiss copy) which all turned out to be sturdy and reliable, and were much appreciated by users. However all those, as the Scotti MGs, fired from open bolt, so were apt for long bursts without overheating, but were not synchronizable.
In the meantime, the Breda SAFAT, having won his competition, remained at the level of evolution it had in the early '30s (good for those years, but no more at the end of the decade) without attempts to adapt it to a more powerful cartridge (as the 13.2X96 used on Breda-31) or to lighten it further.
It must be said, however, that all the Breda and Scotti MGs, with the exception of the Breda-PG, were developed at the specific request of the government, which paid for the prototypes. Both Breda and Scotti demonstrated not having problems in scaling up and down their models. If there was a request of the government for a lighter aircraft cannon, they would certainly have been able to lighten their 20mm autocannons to fire a less potent shell than the 20 X 138b Long Solothurn (for example, the 20 X 105b Short Solothurn, that, firing the same bullet, would have had some manufacturing advantage). But there never was such a request.
The Navy was able to understand that the heavy MG they adopted in '31 for AA defence was rapidly becoming obsolete, and began to replace them with the 20mm Breda 20/65 in 1935. The Air Force did not ask for a 20mm gun adapted to his needs, not even to give to aircraft designers an alternative option to the heavy MGs.
In fact, The competition for monoplane fighter of 1937 nominally required, as a minimum armament, two heavy MGs, or two cannons. That for an assault aircraft, of the same year, nominally required 4 MG, or cannons. But in reality there was no alternative for producers. If they had really wanted to install the cannons, they would have had to adress to foreign products (with the Oerlikon products being the only real possibility, as Italy was under international sanctions), something that certainly did not make the plane more attractive for the decisors, without even being able to really obtain them. In fact, in the prototype of the Ambrosini SS4, where a cannon (most likely a MGFF) was projected, no cannon was mounted. The supply of weapons, as that of the engines, was in charge of the Air Force, and only if the prototype had been accepted, it would have started the procedures to import the guns from foreign manufacturers.
It's worth to say however that, in later '30s, existing 20mm aerial cannons were not so attractive, being, with few exceptions, drum fed and slow firing, so forcing the aircraft to still have at least a couple of supporting MGs, for when the gun end the shots, and for deflection shooting.

 

[Dogwalker]

Because you cannot get this.....
Isotta Fraschini Scotti 20mm

or this....
Breda 35 20mm

...into a Macchi.

But it's interesting to see what's if they tried.
The 12.7mm Breda SAFAT weights 29kg, so the couple weights 58kg, plus 76 kg for 740 rounds in two 370 ammo belt (total weight of the armament, 134kg), the gun fires a 36g projectile at 765m/s at 700rpm (575rpm synchronized) so it has rounds for 32 or 39 seconds of fire (a very long time in WWII).
A Breda 20/65 weights 72 kg, 70kg if we remove the flash suppressor and the secondary sight, (other lightenings are surely possible, as an aero cannon do not needs the massive barrel capable of firing several hundreds of shells prior to overheating, the weapon is excessively robust, to avoid damages during transport, and so on, but lets stay with a 70kg weight), an eventual 200 round belt will weight 56kg (ammo) plus 7kg (links) for a total weight of 133kg for the armament. The gun fires a 130g (average) projectile at 840m/s (average) at 500 rpm (maximum cyclical rate), so it would have rounds for 24 seconds of fire (still a long time in WWII).
So, to get a single Breda 20/65, even without lightenings, into a Macchi, in place of the two Breda-SAFAT, would not have lead to an increase in weight. The gun is capable of fire a round every 2.3 rounds fired by the couple of Synchronized Breda-SAFAT, but this single projectile weights 57% more than 2.3 12.7 X 81 projectiles, and that weight is concentrated into a projectile with a better ballistic coefficient, fired at a far superior speed, so with a flatter trajectory, better penetration, and a far greater range.
As for explosive content, the Breda SAFAT used mostly 3 kind of ammo, AP, ball and HE, traciant or not. The HE round contains 0.8g PETN, so assuming to use the three kinds equally, 2.3 rounds contain an average of 0.6g PETN.
The Breda 20/65 used mostly 3 kind of ammo, AP-T self-destructing (2.4g PETN activated by the traciant tail), AP-E (3.6g PETN activated by an aft placed impact fuse) and HE-T self-destructing (6g PETN activated by an impact fuse, or by the traciant tail; the HE content raised during the war), so, assuming to use the three kinds equally, the average explosive content of a single round is of 4g PETN, 6.7 times the average content of 2.3 12.7X81 rounds.

So, armed wit a single Breda 20x65 in in place of the two Breda-SAFAT, the fighter fires more material, more accurately, at a greater range, with a greater penetration, and hit harder.

But naturally, at the end of the '30s, it was not possible to speculate about a wing mounting for such an heavy (and hard recoiler) weapon on the light Italian fighters. The only possible place for it to be placed is between the cylinder banks of an in-line engine, firing through the propeller hub.
Or mounted where there wasn't a propeller, as in the nose of an Ambrosini SS4 or an IMAM Ro.57.
Even better, due to the low wingload of the SS4, or the 1800hp installed in the Ro.75, is possible to hypothesize even to mount a couple of them without affecting much the aerobatic of the planes (infact the first was designed for three weapons, and two adjunctive MG151/20 were successfully installed in a prototype of the second).
So, why not to install them on those planes?
Cause the Breda 20/65 and the Scotti 20/77 were tray fed. To make them belt fed is a simple modification (infact, belt fed prototypes of the two weapons were made during the war, the modification from drum-fed to belt-fed made to other 20mm cannons was far more complicate), but an aircraft manufacturer couldn't do it. It has to be done by the weapon manufacturer, and first the belt itself has to be projected.
As we know, after the examination of the blueprints, the aircraft prototypes were requested, and paid, by the Air Force, which also had to supply the engines and the weapons.
So, designing a prototype for one or two belt-fed Breda 20/65, or Scotti 20/70, means to design an aircraft for a non existing weapon, hoping that, after examining the blueprints, the Air Force will be so impressed to order to Breda or to Scotti - Isotta Fraschini to build it.
It' obvious that the designers believed to have much more possibilities designing aircrafts for existing weapons.

 

[bruno_]

Interesting considerations. Thanks.
Beside the availability vs unavailability factor, I think people could have been concerned about the gun stoppage scenario: a severe drawback for the single cannon option.
Another point is about the effectiveness of explosive shells. What happens to the destructive power of HE shells when doubling the amount of explosive charge they contain? And, beside the explosive quality and quantity, what other factors could influence the HE shell effectiveness?
I would be grateful to anybody could help on this subject.

 

[Dogwalker]

Interesting considerations. Thanks.
Beside the availability vs unavailability factor, I think people could have been concerned about the gun stoppage scenario: a severe drawback for the single cannon option.

Thanks to you.
That's true, but we can do some consideration. It's sure that the stoppage of both the MGs seems to be a much improbable scenario than that of the single cannon, and, at that time, it was probably a strong argument in favor of the pair of machine guns. But the probability of stoppages raise with the time the weapon fires.
We know, from pilots' accounts, that, with the coming of the four engined bombers, they often ran out of ammunition (and that means they fired against enemy aircrafts for a total of 39 seconds!) trying to shoot them down.
When Minguzzi flew with a Dewotine D520 for the first time, he was surprised to have been able to shoot down a B24 shooting at him "only" the ten rounds he had for the cannon (infact, the fighter was delivered with only ten rounds for the cannon, instead of the 60 of at least an entire single charge of the drum).
With the benefit of hindsight, when the four engined bombers became the main opponents, a fighter could be more effective (and safer for the pilot) firing only for a couple of seconds with the single cannon, and then having it jammed, than firing, for a total of 30 seconds or more, many short bursts to many different targets with the MGs (clearly, the MGs were effective if the pilot could place long bursts on target, but this was more difficult against the fighters, and more dangerous against the bombers).

.

 

[bruno_]

I agree: by 1943 it was "crystal clear" even to several Air Ministry "big shots" that 20mm or heavier cannons had to be considered for effectively intercepting heavy bombers. Just a little bit too late . Moreover the effective range of high muzzle velocity cannon shell had the advantage to start firing outside the effective range of bombers 12,7mm guns. But entering a bomber box was a totally different and very risky business!

Nevertheless at the time specs about standard armament were issued, gun jamming was a crucial point and, beside the intrinsic features of a gun model, people was really concerned about the influence of wild aerobatic on the overall reliability of the whole gun system (gun + cartridges + belt feed layout). This "obsession" was reflected in the dual (mechanic and penumatic) anti-jamming mechanism that was a standard for the couple of 12,7mm guns of wwII italian fighters.

 

[Dogwalker]

As a curiosity. We can remember that, for the P.119, was planned the installation, of a "Breda CL.20" cannon (sometimes referred as "Breda AVID"), with 110 rounds, firing through the propeller hub.
I know no more of this weapon, nor I know if it was installed in the prototype (it should have been, given that the prototype made fire trials), but, in the drawings, its shape seems just that of a Breda 20/65