Alternative airborne guns

[Shortround6]

The rockets were a more versatile answer in practice with the firepower of a single broadside from a light cruiser.

It is a great quote but it is far from accurate.
Pretty much on par with the Mosquito carrying the same bomb load as a B-17 to Berlin.
Light cruisers could vary from five 6in guns to 12 guns in British service and from four 5.5in to fifteen 6in guns in other navies.
5.9-6in gun shell weights varied from 88lbs (?) to 130lbs. British were usually from 100lbs to 112lbs.
Standard British 4.7in destroyer shells weighed 50lbs but naval shells carried less HE per pound than the rockets did.
British cruisers could average about 6 broadsides per minute so you need 6 rocket firing aircraft per minute to really equal even small light cruisers (Leanders and smaller)
BTW, Dido class 5.25in shells weighed about 80lbs each but with less HE than the rockets.

Wiki has a picture of a Typhoon with 60lb type F HE warheads (4.5in artillery shells) but it won't transfer over.

 

[yulzari]

It is a great quote but it is far from accurate.
Pretty much on par with the Mosquito carrying the same bomb load as a B-17 to Berlin.
Light cruisers could vary from five 6in guns to 12 guns in British service and from four 5.5in to fifteen 6in guns in other navies.
5.9-6in gun shell weights varied from 88lbs (?) to 130lbs. British were usually from 100lbs to 112lbs.
Standard British 4.7in destroyer shells weighed 50lbs but naval shells carried less HE per pound than the rockets did.
British cruisers could average about 6 broadsides per minute so you need 6 rocket firing aircraft per minute to really equal even small light cruisers (Leanders and smaller)
BTW, Dido class 5.25in shells weighed about 80lbs each but with less HE than the rockets.

Wiki has a picture of a Typhoon with 60lb type F HE warheads (4.5in artillery shells) but it won't transfer over.

As I said, for a single broadside. 'Light cruiser' is a practical shorthand for a bit less than many cruisers but more than most destroyers. The point is that a full set of 8 rockets is a very big bang, if somewhat spread about. A far bigger bang than a single 6 Pounder bang. I agree that there is a touch of hyperbole in my text.

 

[Shortround6]

Two MG FFMs in the wing might've offered less drag than the twin MG 131 installation of the 109s.

True but the 109G installation was not a good one. Late Gs (?) and Ks got a lower drag cowl. maybe not as low drag as the early Gs with 7.9mm guns but better than the G-6.

The triple MG FFM battery, belt-fed, and a lot of ammo should've been much lighter than the suggested 2x Ho-103 and 2x Type 99-2 battery for the Zeroes, that were very light on power, and indeed under 1000 HP early on.

I am figuring a Zero at about 240kg for two Ho-103s with 250rpg and two Type 99-2s with 100rpg in the drum/magazine.

For the Bf 109 with 1300 HP engine (and any similar mid-war fighter), the triple FFM battery would've been a great fit.

A lot depends on the ammo, both type and quantity.

Better than the Spitfire Vb with two Hispanos and 4 .303s

Weight of guns/drums and ammo is about 243 kg. Weight of a Vc is about closer to 280-290kg, in part due to the extra 31kg of ammo.

or the Zero with the suggested battery

A6M2 with two 12.7s and two Type 99s with 60 round drums would be carrying about 178kg of guns, drums and ammo. See the above weights for something in-between.

Ki-61 with the similar firepower.

This gets tricky.
Very few Ki-61a were built with two 7.7s and two 12.7mm guns
Four 12.7mm Ho-103s with 900 rounds of ammo is 164kg.
Ki-61s were built using two 12.7mm and 250rpg(?) for about 86kg PLUS two German MG 151, gun weight about 84kg for the pair. MG 151 weight includes the belt feed, the electric charging device and electric trigger. What the Japanese used might be subject to question. Amount of ammo per gun was?
MG 151 fired at 700rpm and fired at similar velocity to the Type 99-2 using somewhat lighter shells. I have no idea how much Mineshell ammo the Japanese got.
Using MG FFs or type 99-1s when you have MG 151s is a poor choice. The more ammo you want to use the smaller the total weight difference is. the weight difference between a Type 99-1 with 60 round drum and the MG 151 is around 45-50 rounds of ammo. 150 rounds of the short 20mm stuff is around 27kg without drums or belt links. Saving 8kg per gun (with a belt feeder) is peanuts.

Now not to leave the US out of it.
P-40B ( two .50s and four .30s) was carting around 272kg of guns and ammo and the P-40E was carrying around 408kgs of guns and ammo.
And we wonder why the P-40 had problems

 

[Shortround6]

As I said, for a single broadside. 'Light cruiser' is a practical shorthand for a bit less than many cruisers but more than most destroyers. The point is that a full set of 8 rockets is a very big bang, if somewhat spread about. A far bigger bang than a single 6 Pounder bang. I agree that there is a touch of hyperbole in my text.

It wasn't your hyperbole
That quote has been around since before either of us was born.
Broadside of a destroyer didn't sound as cool.

 

[Gilder]

If it helps the British used rockets with the AP rounds against German shipping. Hits were described as being wet hits (striking the water just short of the hull) or dry hits when they hit above the waterline.

Wet hits caused holes below the waterline and therefore flooding. Dry hits penetrated the superstructure and the continuing rocket burn, would start fires.

Comments have been made about accuracy. Whilst no one would pretend that the rocket was accurate when shooting at a small target such as a tank, any worthwhile naval target is a lot bigger and more than one hit per pass was possible depending of course on the size of the target.

Off France four RN minesweepers were attacked by a squadron of Typhoons, two were sunk and the other two badly damaged. One other victim was the Z24 a large modern 2,600 ton destroyer. Some very large merchant ships were also sunk. Targets which would have only been lightly damaged by a 3in gun, unless of course they were very lucky.

Edit
A comment about the accuracy of the rockets. In January 1945 16 Mosquito's attacked two convoys totalling five merchantmen escorted by five flak ships. One of the merchantmen was hit by thirty rockets and sank, another damaged.

 

[Clayton Magnet]

How much sooner could the Soviets have gotten the Berezin B-20 into service? Seems to be a relatively straight forward modification to the existing UB machine gun, which was in service before Barbarossa.
I REALLY like the concentrated firepower of the Yak-3P, as an almost ideal fighter armament for the time period. 3 centrally mounted, fast firing and light weight B-20 cannons ticks a lot of boxes

 

[bf109xxl]

How much sooner could the Soviets have gotten the Berezin B-20 into service? Seems to be a relatively straight forward modification to the existing UB machine gun, which was in service before Barbarossa.
I REALLY like the concentrated firepower of the Yak-3P, as an almost ideal fighter armament for the time period. 3 centrally mounted, fast firing and light weight B-20 cannons ticks a lot of boxes

The B-20 was not reliable enough - it was never brought up to the required standard.

 

[Shortround6]

The B-20 was an interesting gun.
As a light 20mm gun it has a lot of pluses.
However, some of its minuses don't get covered much.
In recent years (somewhere in the last 20 years) it seems to have lost around 10% of it's velocity (same for the ShVAK) vs what was claimed from WW II to about 2000.
In installations that require synchronization it doesn't seem that the firing rate is adjusted downwards when estimating the firepower.
To be fair many writers fail to do that for other guns, US .50 was notorious for not getting close to rated RPM when synchronized.

 

[Admiral Beez]

Was there any heavier gun that could be made for the Bréguet 693? A single 20mm and two 7.5mm machines guns does not seem sufficient forward armament even for a 1939-40 ground attack aircraft. The obvious answer is to add another (or more) 20mm cannons, but was there anything else? There's the heavier 13.2 mm Hotchkiss machine gun that could replace the two 7.5mm while keeping the single 20mm cannon. Would 2 × HS.404 20 mm cannon and 2 × 13.2 mm Hotchkiss heavy machine guns be too much for this aircraft?

 

[Shortround6]

Would 2 × HS.404 20 mm cannon and 2 × 13.2 mm Hotchkiss heavy machine guns be too much for this aircraft?

In what regard?
The plane was supposed to hold eight 110lb bombs (400kg) inside so there is definitely weight to play with.
If you want a super-strafer you can certainly up the gun load and get rid of the bombs.

Now how historical do you want to stay with? In 1940 the French had drums only for the Hispano gun, but a belt feed was in the works. I see no reason why a larger drum could not have been developed if desired given time.
The 13.2mm Hotchkiss is more of problem. While there are less suitable guns for aircraft use you do have to look hard for them. Anything can be fixed with enough time and money but that doesn't mean you should. The Gun was extremally heavy for it's power, not problem when mounted on a ship, more of problem for solders trying to schlep it over the countryside. A real problem trying to stick in an airplane. Only available in factory form with a 30 round magazine. Possible larger magazine or drum? How much time/money to turn it into a belt feed?
Cycle rate was only about 450rpm, that could be changed but trying to fire a lot faster might be very difficult. Japanese didn't even try. They just copied the US Browning and chambered it for the French cartridge. So did FN in Belgium.
You could try having the rear gunner turn around and try to stuff magazines into 4 different weapons to reload
We can argue about recoil loads but that can be solved with spring mounts and/or local beefing up of structure.

main problem is the sort of lack of performance of the machine. You need a lot more power, which means bigger engines and more weight a redoing more stuff.
None of the 3 engines used were that good and a 10,000lb twin with 304sq ft of wing using roughly 700hp engines was having trouble. Once source says 242mph at sea level at normal gross weight (H-S engines?) 227mph at max gross weight. Roughly 300mph at 16,400ft but strafing seems to be a problem.
Redesigning the plane to use larger engines is possible but that takes time and money, and estimates get a lot more iffy.

 

[bf109xxl]

In installations that require synchronization it doesn't seem that the firing rate is adjusted downwards when estimating the firepower.
To be fair many writers fail to do that for other guns, US .50 was notorious for not getting close to rated RPM when synchronized.

According to the official manual, the RoF of the B-20 on the La-7 ranged from 750 to 850 rpm, which was quite sufficient. The main problem was its low reliability, which led to the rapid replacement of the B-20 with the NS-23. Another problem was the low-power ShVAK cartridge.

 

[Elan Vital]

Interestingly enough, the British requirements for Hispano-Suiza cannon adoption from February 23rd 1940 include 4 cannons per Spitfire III from September 1940 onwards, with an inferred production of this aircraft of 75 in September, 100 in the next months and 105 in January 1941. Although a note states that it is not certain that this aircraft can use this armament. It goes to show that this heavy armament was envisionned quite early.

 

[Shortround6]

British were envisioning four 20mm cannon fairly early. Some of the Aircraft competing with the Hawker Typhoon/Tornado show four 20mm cannon. Brand differed and they show drums at that point and trying to fit 2 guns in each side with drums was not easy. Britian had signed up for both the H-S and Oerlikon fairly early with H-S gun being favored for air use and the Oerlikon favored for surface/ground use. But it took around 2 years to build/equip a factory so desired goals were often not met.

 

[Elan Vital]

A related question about the British H-S, did they produce them themselves as of early/mid 1940 or were they reliant on the French factory? If the latter, I assume that the Fall of France disrupted supplies of this gun for some time

 

[Shortround6]

A related question about the British H-S, did they produce them themselves as of early/mid 1940 or were they reliant on the French factory? If the latter, I assume that the Fall of France disrupted supplies of this gun for some time

Britian had signed some contracts in Jan 1938 created British Manufacturing And Development Company (British MARC or BMARC)'
June 1938 saw the land deeds for the factory land registered, machinery purchased in Britian and the US.
Dec 1938 saw a few guns leave the assembly lines, British workers using metric drawings.
Jan 1939 saw the official opening with the Duke of Gloucester firing the first British HS-404.
By mid 1940 it was obvious that the original factory was not big enough and
a second factory was built in Grantham next to the original.
a third at Newcastle-under-Lyme, directed by BSA
a fourth specifically for HS-404 production at Poole.
a fifth at the Enfield Royal Small Arms facilities.
I don't know when any of these joined in the production plans.
A British officer (name escapes me at the moment) escaped with the belt feed drawings from France at the end of June and the British fooled around for months (maybe 9?) coming up with alternatives before giving in and adopting the basically the French system. British did not like the French system because it pressed on the nose of the shell to push the rounds out of the belt. The pneumatic system trialed in a Whirlwind was ingenious, but it used air many times faster than planned and the on board air compressor had no hope of keeping up with multiple guns.
The HS-404 was not actually a finished product. It had been designed to be bolted onto a V-12 engine and without that support it tended to malfunction. It was also designed to lubricated ammunition to function correctly and the lubrication (oil or grease) caused problems at low temperatures/high altitudes. British came up with a wax coating that could be applied at the factory and not depend on the squadron armorers to oil/grease the cartridges before loading. British also shortened the chamber by 1 (2?) mm to jam the cartridge into the chamber harder which increased the firing pin impact for more reliable ignition (Americans didn't believe the British and used the original French drawings).
The gun had been designed to last 10,000rounds before overhaul (not barrel life) and this was allowed to decrease to 2,000 rounds on the faster firing MK Vs.
British 2nd tactical air force used 13.5 million rounds of 20mm ammo in the last year of the war. That is over 1750 metric tons of 20mm projectiles.
You have to plan to supply the guns.

 

[Elan Vital]

In what regard?
The plane was supposed to hold eight 110lb bombs (400kg) inside so there is definitely weight to play with.
If you want a super-strafer you can certainly up the gun load and get rid of the bombs.

Now how historical do you want to stay with? In 1940 the French had drums only for the Hispano gun, but a belt feed was in the works. I see no reason why a larger drum could not have been developed if desired given time.
The 13.2mm Hotchkiss is more of problem. While there are less suitable guns for aircraft use you do have to look hard for them. Anything can be fixed with enough time and money but that doesn't mean you should. The Gun was extremally heavy for it's power, not problem when mounted on a ship, more of problem for solders trying to schlep it over the countryside. A real problem trying to stick in an airplane. Only available in factory form with a 30 round magazine. Possible larger magazine or drum? How much time/money to turn it into a belt feed?
Cycle rate was only about 450rpm, that could be changed but trying to fire a lot faster might be very difficult. Japanese didn't even try. They just copied the US Browning and chambered it for the French cartridge. So did FN in Belgium.
You could try having the rear gunner turn around and try to stuff magazines into 4 different weapons to reload
We can argue about recoil loads but that can be solved with spring mounts and/or local beefing up of structure.

main problem is the sort of lack of performance of the machine. You need a lot more power, which means bigger engines and more weight a redoing more stuff.
None of the 3 engines used were that good and a 10,000lb twin with 304sq ft of wing using roughly 700hp engines was having trouble. Once source says 242mph at sea level at normal gross weight (H-S engines?) 227mph at max gross weight. Roughly 300mph at 16,400ft but strafing seems to be a problem.
Redesigning the plane to use larger engines is possible but that takes time and money, and estimates get a lot more iffy.

FWIW Breguet designed the Breguet 700 heavy fighter which was a 691 redesigned around G-R 14N 48/49 engines and apparently the nose armament was modified to 4 20mm cannons with 90 rpg and 2 7.5mm MGs with 500 rpg, without the bomb bay. So a 90 round drum magazine apparently was a thing.

 

[ThomasP]

re a 90-round drum feed

IIRC the French were about to field a belt-feed mechanism for the HS404 (or whatever equivalent model they were using) in several of their next series of single-seat single-engine fighter variants when the war ended. Could this be the reason for the 90-rounds per gun?

 

[Elan Vital]

re a 90-round drum feed

IIRC the French were about to field a belt-feed mechanism for the HS404 (or whatever equivalent model they were using) in several of their next series of single-seat single-engine fighter variants when the war ended. Could this be the reason for the 90-rounds per gun?

Most French sources state 120 rpg for belt-fed 20mm mountings.

 

[Elan Vital]

The Docavia on French fighters itself mentions that a 100-round drum magazine for the 20mm had been tested without success, while the belt-feed had been tested for mountings of up to 200 rounds per gun. Shorter barrels like what the British eventually fielded were envisioned.

 

[MIflyer]

I think this would have been a superior installation than the standard one, at least relative to the nose guns. But for strafing Japanese ships the extra gun pods probably would have been very useful, too.