Why Mixed Armament?

[MK-84]

Just like the title says.  Some aircraft use the same armament throughout, many of the US planes with .50s.  Some I can understand like an Il2 where there are specifically different roles with each weapon.  But others like spitfires, FW190s and most of the fighters with cannon/MG armament I dont get.

Is it due to space concerns? or manufacturing availability, or a designed on purpose for reasons I do not get.

[EagleDNY]

The "different weapons for different roles" argument really works for all of them - not just the Il-2, and I think what you seeing is just the progression towards heavier and heavier armament.  The .30 (7.92mm) MGs proved early on to be inadequate because of the vastly increased speed of air combat, so the Germans and the British went to 20mm.  I think part of this is just the history of weapons development - the British and French had the Hispano 20mm early on, so once you standardize it is just a question of making a lot of them and fitting them as appropriate.  The Germans had the early Oerlikon 20mms as their starting point, and developed the MG-151 from that.  The Germans needed stuff that would knock down big bombers, so they went to 30mm and tried stuff heavier than that as well.   You see even bigger stuff on the ground attack side (37mm, 40mm, etc). 
The Americans had the .50 cal from the beginning, and it might not have the explosive power of a 20mm shell, but it puts out a lot of lead and has decent light armor penetration.   If the Japanese had started sending over their version of B-17 raids, maybe we would have ended up with 4 x 20mms Jug, or the development of the 37mm P-39 Olds cannon into a gondola mount.  Since they were only fighting lightly armored planes though, the .50s were plenty - especially when you put 6 or 8 of them together. 

I do sometimes wonder why (given the amount of weaponry we were sending the British in 1940-41) they never put the .50 cal to use in Spitfires and Hurricanes.  6x .50s in a Spitfire would be an ugly thing to have on your tail.  I'll have to do a little looking to see if they ever gave it a tryout.   

[titanic3]

Because in real life, a single bullet can mean life and death. A 7.9mm can do a lot of damage that is not shown in AH and just the fear factor of constantly having rounds being shot at you was a big deal. The cannons were more effective, but planes could only carry so much. By replacing 1 cannon for 2 MGs, a pilot had more firing time and more chances to do damage. In AH, we do not have luck as a factor in the damage models and no partial damage. A single 7.9mm could rip a hydraulic line or kill the engine if well placed or was a lucky round. In AH, a single 7.9mm is nearly useless unless aimed DIRECTLY at the pilot.

Also, there were plenty of ground targets that did not require high caliber rounds to cause damage. Trucks, trains, barges, cargo ships, and infantry were all attacked. In AH, we use a point system for damage where once you pass a "point", the object is destroyed, therefore, cannons are a much more suited to ground attacks. Again, in real life, a single 7.9mm can cause a lot of damage and a lot quicker with a higher RoF.

[Oldman731]

Is it due to space concerns? or manufacturing availability, or a designed on purpose for reasons I do not get.

Weight, and find-a-place-to-put-it.

- oldman (mostly weight)

[Karnak]

P-39D has to be the worst.  One 37mm cannon, two .50 caliber machine guns and four .303 caliber machine guns, none of which have remotely the same ballistics.  The thing was a damned flying pre-Dreadnought.

Not sure about the Germans and Japanese, but for the British the 20mm Hispano Mk I in the Spitfire Mk Ib and Mk IIb was extremely unreliable and they were concerned that a fighter armed only with cannons could find itself unarmed by jams.  In the actual event the cannons did not jam excessively once the better mount was introduced with the Mk Vb, but at that point the machine guns were there and still somewhat useful.

I do sometimes wonder why (given the amount of weaponry we were sending the British in 1940-41) they never put the .50 cal to use in Spitfires and Hurricanes.  6x .50s in a Spitfire would be an ugly thing to have on your tail.  I'll have to do a little looking to see if they ever gave it a tryout.    

The RAF determined in the 1930s that the rifle calibre machine gun was not going to be adequate.  In looking for future weapon systems they decided that the heavy machine gun would only be a stopgap and instead of spending time on it they would go directly to shell firing cannons.  There were some delays in getting the cannon into service though.

(We also didn't send much of anything to the British in 1940, though the 100 octane fuel we sold them was very useful.  Lend-Lease was a 1941 program, but by then the Spitfires were armed with cannons)

[save]

Fw190a5 have 2 7.9mm 2 20mm ff 2 mg151 , all have different trajectory

[Rob52240]

I know the English planes using .30 cals have the 30's because the US couldn't keep up with Browning M2 .50 demand.

[Karnak]

I know the English planes using .30 cals have the 30's because the US couldn't keep up with Browning M2 .50 demand.

Not true.

[Rob52240]

Not true.

Were they spec'd by idiots?

[titanic3]

I would thnk that it's a moot point about ballistics because they can all be set to converge at the same point. Only once you get past the point of convergence does the ballistics becomes a hindrance in aiming.

[Karnak]

Were they spec'd by idiots?

Read my post from above.  In the 1930s the RAF determined that the heavy machine gun would be inadequate and nothing more than a stopgap upgrade to the rifle caliber machine guns they were already using.  Based on that they decided to go directly to the 20mm cannon as the next standard weapon in the RAF.  In addition, arming aircraft with the heavy machine guns would complicate logistics by adding a third ammunition type to be stocked.

No, they were not idiots and had correctly identified the heavy machine gun as an inadequate weapon.

[Rob52240]

In the US it is commonly believed that it was due to a shortage of M2 machine guns.

It makes sense for late war, but I like your explanation better.

[bozon]

Different armaments for different purposes: 20mm to down planes, 0.303 to shoot the chutes after they bail.

[STXAce8]

Also I believe I heard somewhere the Germans just wanted to shred whatever they had a shot at and the Americans just  wanted to get the plane out of the fight, or so I heard....

[Charge]

When you operate over enemy territory you need to destroy your target to be sure he does not ditch and the plane won't get repaired. If the pilot gets killed in process so that you do not need to make a moral choice of shooting him in chute would be a convenient plus.

During BoB .303 was adequate to cause damage so that German planes that got out damaged usually ditched into Channel. However, many still got away so 20mm with its ability to cause catastrophic structural damage was desired.

During battle of Germany the US would have been better off with 20mms considering destructiviness but .50Cal was reliable and ammunition readily available and easy to supply overseas and to units. There was also trouble with US 20mm but problems with its realiability hindered its introduction and in that operative situation even .50Cal was pretty much enough. The introduction of 20mm to US service was then delayed to Korean conflict and beyond.

I think the armament of FW190s is a good example of how necessity dictates what will be put on plane and what would not. First the outer wing MG FF got dropped out due worse ballistics and small ammo load to regain competiviness in speed and maneuverability. After outer positions got updated to MG151/20E in A6 the MGs were not dropped out but updated to 13mms in A7 with wider variety of ammunition types but still the outer position was kept empty in some machines (as in D9s) for improved performance. I'd say that it was considered that any amount of rounds that were thrown against bombers would increase to possibility of fire or crew casualty and they also gave a slight possibility for defence once 20mms were expended in a fighter versus fighter fight. However during the introduction of both ground attack variants and recce versions the MGs were dropped out and only the inner wing MG151/20Es retained. MK108 would have been a decent gun for inner wing positions but it was not available in positions that needed synchronized action so they were carried in outer positions only and preferred for bomber interception.

-C+