Impact of fully adopted and reliable 20mm in BoB

[pbehn]

I always thought the US .50 cal was a good gun, from essentially the start.

Back to cannons, how we're the Japanese 20 mm cannons for reliability?

Guns and ballistics aren't my "bag" but as I understand it for the British in 1940/41 switching to 0.5" mgs would hardly have been an improvement. Its reliability, rate of fire and I think muzzle velocity were transformed between 1940 and 43. The RAF did eventually put them on Spitfires because the ballistics were closer to the 20mm cannon. Its a bit like comparing a Merlin in 1940 to one in 1943, the name is the same, almost everything had changed.

 

[Shortround6]

I always thought the US .50 cal was a good gun, from essentially the start.

when is the start?
There are a lot of posts and threads on this.
The M2 changed rates of fire in 1940 without changing designation. went from 600rpm (if you were lucky and using a short belt of ammo) to about 800rpm.
At some point ( I believe it was after the change in rate of fire?) they doubled the weight of the belt pull (amount of weight of ammunition the gun would lift from a certain height)
about 1940 the US changed the Propellent (British continued to buy the old specification ammo) and raised the velocity of the bullet from 2500fps to 2880fps.
There were also changes in projectiles. A 1943 M2 .50 cal is a rather different weapon than a 1940 M2 .50 cal.
And this doesn't count the differences in gun heaters or feed boxes or....................................

Back to cannons, how we're the Japanese 20 mm cannons for reliability?

The Japanese Navy type 99-1?
The Japanese Navy type 99-2 (used different ammo, 29mm longer cartridge case)?
The Japanese Army Ho-1/3? used it's own ammo
The Japanese Army Ho-5? another type of ammo.

 

[Glider]

That's the trouble with the Whirlwind and its four cannons. With only 60 rounds per gun, for a total of 240 rounds, each gun firing 600–700 rpm, you'd need burst control to avoid needlessly avoid depleting all your shells into that first bomber. We need earlier belt feed systems for the Hispano-Suiza.

It should be remembered that the 109E only had 60 rpg so the problem wasn't limited to the RAF early 20mm

 

[Greyman]

Unfortunately this deals almost entire with enemy fighters, not bombers, but here is an analysis the RAF made of 1871 fighter sorties during a select period in 1941.

After crunching the numbers they arrived at:

Number of RAF fighters engaged for every enemy aircraft destroyed

5.17 - 8 Brownings​

4.00 - 12 Brownings​

2.50 - 4 Brownings, 2 Cannon​

Number of enemy aircraft engaged for every enemy aircraft destroyed

9 - 8 Brownings​

10 - 12 Brownings​

5 - 4 Brownings, 2 Cannon​

Number of RAF fighters destroyed for every enemy aircraft destroyed

.364 - 8 Brownings​

.471 - 12 Brownings​

.261 - 4 Brownings, 2 Cannon​

Based on claims, obviously -- but I think it gives a reasonable indication of the efficacy of cannon.

EDIT: I imagine the 12 x Browning figures are skewed somewhat in the fact that they are all Hurricanes, whereas the great majority of 8 x Browning fighters would be Spitfire IIs -- and so a better comparison for the cannon-armed Spitfires.

 

[Admiral Beez]

The Japanese Navy type 99-1?
The Japanese Navy type 99-2 (used different ammo, 29mm longer cartridge case)?
The Japanese Army Ho-1/3? used it's own ammo
The Japanese Army Ho-5? another type of ammo.

It's amazing how those two services couldn't get along or share tech and kit. I wonder if the IJN and IJAF pilots had separate barracks when they had to share bases, like at Rabaul. The British FAA and RAF weren't on best terms, but they shared the same aircraft guns, ammunition, engines, etc. and many of the same aircraft types. IIRC, the only purely naval fighters of British origin, with no RAF equal from the beginning of British naval aviation until the jet age were the Flycatcher, Fulmar and Firefly. The Japanese founded their carrier force on the British model, but thought that a small island nation with limited resources should instead run a completely separate air arm for its navy, with separate guns, aircraft, etc. Imagine the logistics, how often did a crate of 20 mm cannon ammunition arrive at a base only to be non-compatible?

 

[The Basket]

If the RAF used a 20mm cannon then I would ask how many in each fighter?

So let's say 2 cannon per Spitfire so I would then say how many rounds of ammunition per gun and how long firing time? How many 303 are retained?

How quick firing? You only have a moment to aim and fire so a slow firing cannon could be a burden. Many pilots were not combat ready and had very little trigger time so having a slow firing cannon which needs a more expert shooter especially at range can be a disadvantage.

If 20mm and 303 is kept then you have 2 guns with different ballistics making training worse.

Better a hit with 303 than a miss with 20mm and you can spray and pray with 303 which you can't do with 20mm especially if you're green around the gills.

The conversion of 303 to 20mm has some flaws.

 

[Admiral Beez]

If the RAF used a 20mm cannon then I would ask how many in each fighter?

My thinking in the opening post was an earlier introduction of what we saw. So, Spitfire Mark V's 4 x .303 mg and 2 x 20 mm cannon, and the Hurricane's 4 x 20 mm cannon. It would however be interesting to see how Hawker could accommodate the same armament as the Spitfire Mk. V.

 

[Kevin J]

My thinking in the opening post was an earlier introduction of what we saw. So, Spitfire Mark V's 4 x .303 mg and 2 x 20 mm cannon, and the Hurricane's 4 x 20 mm cannon. It would however be interesting to see how Hawker could accommodate the same armament as the Spitfire Mk. V.

The Russians modified the Hurricane II to carry 2 x 20 mm cannon and 2 x fifties.

 

[swampyankee]

Some Spitfires also carried two 20 mm Hispanos and two 0.5 in MG. I believe the preference was for four 20 mm, but the design of the Spitfire's wing (at least in some variants) made it difficult to adequately heat the weapons bays for four 20 mm.

 

[Admiral Beez]

Some Spitfires also carried two 20 mm Hispanos and two 0.5 in MG. I believe the preference was for four 20 mm, but the design of the Spitfire's wing (at least in some variants) made it difficult to adequately heat the weapons bays for four 20 mm.

I like this idea of 4x20mm cannon armed Hurricane with the Douglas Boston spotlight.

Hawker Hurricane Mk II as Nightfighter

 

[Admiral Beez]

The ultimate cannon armed Hurricane wouls have been the IIc with 40mm cannon pods, but we never see these in combination with the four 20mm cannons. Perhaps too much weight or recoil?

 

[Admiral Beez]

Some Spitfires also carried two 20 mm Hispanos and two 0.5 in MG. I believe the preference was for four 20 mm, but the design of the Spitfire's wing (at least in some variants) made it difficult to adequately heat the weapons bays for four 20 mm.

Check out this Spitfire with six cannons! If only a dummy installation as a weight/aerodynamics trial.

Guns & Cannon: Rules of Thumb

 

[Kevin J]

Check out this Spitfire with six cannons! If only a dummy installation as a weight/aerodynamics trial.

Guns & Cannon: Rules of Thumb

The story one of my teachers at school told us all was that a Spitfire with 4 x 20 mm cannon and 4 lmg was tested over the the river Thames. I grew up, went to school in Westcliff on Sea, on the Thames Estuary. That the wings broke off, and it lies under the water out there.

 

[fastmongrel]

The story one of my teachers at school told us all was that a Spitfire with 4 x 20 mm cannon and 4 lmg was tested over the the river Thames. I grew up, went to school in Westcliff on Sea, on the Thames Estuary. That the wings broke off, and it lies under the water out there.

Sounds like an urban myth. If the wing was passed to carry 4 x 20mm Hispano (Spits with the C or E wing could carry 4 x Hispano) the extra recoil of 4 x Browning .303s would be barely noticeable.

Guide to Spitfire wing types

 

[Kevin J]

Sounds like an urban myth. If the wing was passed to carry 4 x 20mm Hispano (Spits with the C or E wing could carry 4 x Hispano) the extra recoil of 4 x Browning .303s would be barely noticeable.

Guide to Spitfire wing types

Quite possibly, but 4 cannons only became standard with the Mk 21 onwards, before that it was 2 cannon plus either no mg, 4 lmg or 2 HMG. 4 cannon + 4 lmg is a lot of recoil for such a slender wing.

 

[The Basket]

Get annoyed when people say the 8 303s is weak sauce.

No it ain't. Plenty good enough.

Ain't pop guns.

 

[Admiral Beez]

Get annoyed when people say the 8 303s is weak sauce.

No it ain't. Plenty good enough.

Hawker Hurricane IIB and its 12 x .303s wants a word.

It's interesting how the Japanese thought a pair of .303s was sufficient in the early Ki-43 when the British were stuffing guns into every nook.

 

[Shortround6]

It's interesting how the Japanese thought a pair of .303s was sufficient in the early Ki-43

In part due to problems with the Ho-103 machine gun which included.

1, not enough of them
2, not enough ammo
3, a rather low rate of fire when synchronized.
4, ammo that tended explode in the gun barrel or upon leaving the gun barrel leading to armor troughs (or at least heavy steel) being fitted from the gun muzzle/s forward over the engine.

 

[wuzak]

"Impact of fully adopted and reliable 20mm in BoB"

Even slower Hurricanes?

 

[Admiral Beez]

In part due to problems with the Ho-103 machine gun which included.

1, not enough of them
2, not enough ammo
3, a rather low rate of fire when synchronized.
4, ammo that tended explode in the gun barrel or upon leaving the gun barrel leading to armor troughs (or at least heavy steel) being fitted from the gun muzzle/s forward over the engine.

Goodness. And all this with a .303 type gun that's been flying in pairs since 1915.