Why Mixed Armament?

[EagleDNY]

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.

Was reading that when they conducted the trials in the 1930s they didn't have all the fancy ammo for the .50 that we had later on (1943 and on - API, etc.) and that they were testing the slower firing (600rpm) version instead of the later versions.  Given that, I can see why they would opt for the 20mm Hispano and elect to work out the kinks.

[Jabberwock]

According to Tony William's excellent website, the UK compared the M1924 to the Vickers .50 cal in the ground role 1920s. The Browning as tested, had an RoF of 500-750 rpm.

He also has this to say about the RAF's thinking on the .5 cal:

"The RAF also evaluated the .5 inch Vickers and Browning guns. The results were inconclusive; the Browning was more powerful but was longer and heavier. It was concluded that the .303 inch version of the Vickers was almost as effective as the HMGs against the light, unarmoured aircraft structures of the time and it was much lighter as well as faster-firing. The RAF accordingly decided not to proceed with a heavy machine gun, while noting that any widespread adoption of armour for military aircraft would force a re-think. By the mid-1930s, when the increasing performance and toughness of aircraft began to cast doubt on the future of rifle-calibre guns, the RAF opted for the greater destructive power of a 20 mm cannon, choosing the French Hispano HS 404. A few American .5 inch Browning M2 guns were used late in the Second World War in applications for which the Hispano would have been too big and heavy, but apart from this no heavy machine guns were used by the RAF."

Taken from www.quarry.nildram.co.uk/Vickers.html

[SmokinLoon]

First off, some of you need to learn the difference between ".303 British" and ".30 US" (.30-06 Springfield).  They are 2 very different cartridges.  The US P39 did NOT fire British .303, they fired .30 US.     The Soviets had their own .30 caliber MG round as well.  As did the Germans, French, Japanese, Italians, Austrians, Belgians, etc etc.  In terms of performance, they were all very relatively close especially in terms of air combat.  A 150gr-200gr FMJ bullet flying between 2400 and 2800 fps isn't going to have too much of a spread in term of trajectory and damage performance.  On the ground and against cover and flesh there were some differences, but even then they were all still close.  The mechanism (rifle or MG) that used that cartridge and the rate of fire in which they were sent down range were more important.   

There are lots of theories as to why there were differences in guns and cannons for plane armament.  Most of it has to do with the speed in which WWII progressed.  Remember, when WWII began (officially, at least in Europe), most planes still had .30 cal MG's for their main weapons because they were already available in massive quantities and that has always been the standard.  Once the war progressed, it became evident that the harder hitting guns and cannons were going to be needed.  But even then, production could not keep up with demand nor could it completely convince in the top brass that leaving the .30 cal's behind was the thing to do.  The US got smart quick and standardized the 4 or 6 gun .50's, while much of Europe went fewer guns but with more power per round (enter 20mm HE vs massed .50cal FMJ debate).

There are also theories on aircraft designs being a big influence on which guns were used.  For instance, the Fw190 was designed to have 2 guns in the cowling and 2 guns in the wing, with all 4 guns firing through the prop arc to keep the center of gravity in close to aid in the roll rate, or so I've read in some online writings.  In regards to the P39, it made perfect sense to cram in a 37mm in the nose because it had the room.  Once it was engaged in fighter combat, it was deemed to be "too much".  The P38, the first "bomber interceptor" to be designed as such had quad .50's with 500 rounds per gun available and a 20mm with 120 rounds available for a reason.

IMO, the P39D is not the worst. Yes, it has three different calibers but the trajectories are not all that different.  IMO, the worst is the 190A-8.  Take a look at the differences between all three calibers and you will truly see that having 2/13mm's, 2/20mm's, and 2/30mm's would be a nightmare to hit anything beyond (or nearer if the convergence was set way out) the point of convergence.  The Germans didnt have fast moving projectiles when compared to the US and Brits in any caliber.     

[Jabberwock]

 

 The P38, the first "bomber interceptor" to be designed as such had quad .50's with 500 rounds per gun available and a 20mm with 120 rounds available for a reason.

Well, not really. The P-38 was hardly the first bomber interceptor to be designed, or even the first to be put into production.

P-38 initial armament installations were really quite varied. There was the standard 4 x .50 and 1 x 20 mm set up, but there was also a 4 x .50 and 1 x 23 mm (the Army Ordinance T1/T2 - a close copy of the Oerlikon 23mm) lay out trialed in very early versions, as well as a 2 x .303, 2 x .50 and 1 x 37 mm set up and a 4 x .303 and 1 x 37 mm set up.  There was also an all .50 lay out and even a twin 23 mm layout. They also wanted to fit a 25 mm Hotchkiss aircraft cannon.

The USAAF was still switching between the 20mm ANM2 and the M4 37 mm as late as the P-38E

IMO, the P39D is not the worst. Yes, it has three different calibers but the trajectories are not all that different.  IMO, the worst is the 190A-8.  Take a look at the differences between all three calibers and you will truly see that having 2/13mm's, 2/20mm's, and 2/30mm's would be a nightmare to hit anything beyond (or nearer if the convergence was set way out) the point of convergence.

Ill take the mix of 13, 20, 30 mm over 7.8, 12.7, 37 mm any day.

  The Germans didnt have fast moving projectiles when compared to the US and Brits in any caliber.     

Oh, I think there were a few:

MG 151/15: MV of 960 to 1030 m/sec, that's better than almost any other in-service aerial cannon of the period.
MK 101/103: MV of 840-960 m/sec, which would match, if not slightly better the M2
MG 17: MV of 850-925 m/sec, which is better than the .30 and .303 Brownings

[Jabberwock]

 

 The P38, the first "bomber interceptor" to be designed as such had quad .50's with 500 rounds per gun available and a 20mm with 120 rounds available for a reason.

Well, not really. The P-38 was hardly the first bomber interceptor to be designed, or even the first to be put into production.

P-38 initial armament installations were really quite varied. There was the standard 4 x .50 and 1 x 20 mm set up, but there was also a 4 x .50 and 1 x 23 mm (the Army Ordinance T1/T2 - a close copy of the Oerlikon 23mm) lay out trialed in very early versions, as well as a 2 x .303, 2 x .50 and 1 x 37 mm set up and a 4 x .303 and 1 x 37 mm set up.  There was also an all .50 lay out and even a twin 23 mm layout. They also wanted to fit a 25 mm Hotchkiss aircraft cannon.

The USAAF was still switching between the 20mm ANM2 and the M4 37 mm as late as the P-38E

IMO, the P39D is not the worst. Yes, it has three different calibers but the trajectories are not all that different.  IMO, the worst is the 190A-8.  Take a look at the differences between all three calibers and you will truly see that having 2/13mm's, 2/20mm's, and 2/30mm's would be a nightmare to hit anything beyond (or nearer if the convergence was set way out) the point of convergence.

Ill take the mix of 13, 20, 30 mm over 7.8, 12.7, 37 mm any day.

  The Germans didnt have fast moving projectiles when compared to the US and Brits in any caliber.     

Oh, I think there were a few:

MG 151/15: MV of 960 to 1030 m/sec, that's better than almost any other in-service aerial cannon of the period.
MK 101/103: MV of 840-960 m/sec, which would match, if not slightly better the M2
MG 17: MV of 850-925 m/sec, which is better than the .30 and .303 Brownings

[vafiii]

Good topic. I always wondered why the Spitfire engineers grouped four .303's with the two 20mm cannons? Seems like an odd gun package to me? Why not simply remove the .303's altogether and add more 20mm rounds? The weight would have been comparable and you could have done a hell of a lot more damage.

Also, on the same topic, did Spitfire pilots fire all guns at once or cannon's first and then the .303's once the cannons ran out?

I met an old German 109 Pilot at an air show last summer and he said he only used the nose cannon, not the machine guns. Of course, he had a .30mm in the nose and as he put it, "one shot and they were down."

[smoe]

Have to remember what people know today vs back then are very different. AH2 flyer's can experience every type of aircraft in an almost infinite possible amount of scenarios. Back then a lot of times the learning curve meant you go home or your enemy does, but not both.

If it were 1944 and given a choice of what I know today. I would mount F4U-1C guns in a 51D.

[bustr]

If you read any 8th air force enemy armament reports from WW2 it was their assersion that bomber destruction, then fighter speeds and armor which dictated armament development. The 8th produced reports on the utility of all rounds being used versus their usefullness as the war proceded.

Yes rifle caliber and 50 cal rounds work very well for general ground straffing duties. As noted the 50cal evolved into the API round to take advantage of it's kinetic penetration properties and to start fires if it caused a fuel or flamable liquid leak. The rifle caliber rounds on both sides began to have littel to no effect in peircing fuel tanks or armored areas designed to protect fuel, oil, engine and pilot.

Enter the MG131 with it's mixed bag of special purpose rounds to attempt to penetrate fuel tanks and start fires again. The 8th rated the MG131 as a round for starting fires, then 20mm Hisso/MGFF/MG151\15\20 and MK101/103/108 as possible aircraft destruction and 25% aircraft destructive. The US even looked into the MG151\15 to model a 60cal as a possible replacement for the 50cal to gain HE content in their rounds. Only the US would build a 20mm that the shells needed to be lubed to cycle properly. Hey Joe pass me the Bear grease, the Lewi gets cranky when his guns jam.

Mixed bag of gun types to the 8th at least represented covering the primary methods of destroying an aircraft. Kinetic penetration via numbers of rounds or high speed fragments, fire starting, and explosive destruction. The germans approached this in thier 13mm-30mm with a wide menu of purpose designed round types. AP, API, APHE, HE, Incendiary, Mineshell. British AP, API, HEI, SAPI. Russia HEI, HEI-T, HE-Frag, HEI-Frag, AP, API-HC, API, API-T. Japan AP, API, HE, HE-T. And the US primairly API with the 50cal, HE with it's 20mm.

Kinetic high speed penetration from many types of sources, burning, and explosive destruction.
 
If you cannot carry alot of ammo, carry the best mix you can to achive the broadest amount of possible damage to the specified target type. Or bring a truck load of 50cal.

[Karnak]

Good topic. I always wondered why the Spitfire engineers grouped four .303's with the two 20mm cannons? Seems like an odd gun package to me? Why not simply remove the .303's altogether and add more 20mm rounds? The weight would have been comparable and you could have done a hell of a lot more damage.

120 rounds for each cannon takes the space available.  The .303s are further out on the wing and would free up no additional space that could be used for 20mm ammo.  That said, some pilots did have the .303s taken off to reduce weight.

Also, on the same topic, did Spitfire pilots fire all guns at once or cannon's first and then the .303's once the cannons ran out?

The cannon armed Spitfire's stick had a rocker switch for a trigger where if you pushed on the top it would fire the cannons, the bottom would fire the machine guns and the middle would fire all guns. (I am not sure if the top or bottom was cannons actually)  You can see this switch on the Spitfires in AH actually.  Look at the stick for the Spitfire Mk I, a simple button, and then compare it to any of the cannon armed Spitfire's triggers.

I met an old German 109 Pilot at an air show last summer and he said he only used the nose cannon, not the machine guns. Of course, he had a .30mm in the nose and as he put it, "one shot and they were down."

That does not surprise me in the least.

[Pongo]

Why?
Because they had to. Most of WW2 was fought with airframes designed well before the first shots. Cannons where slow firing and short shooting, you had to have cowl guns to give some length of fire and and some reliability. As the cannons inproved they shoved them every where they could, but some could not be sycronized or being syncronized they would have such a slow rate of fire as to be near useless. That is why the 190 A3 had 7.9mm cowl guns,(could not put cannons there), 151/20 wing root guns(syncronizable) and MgFF outer wing guns , not sycronizable and lighter and more available while 151 production ramped up.

The spit had 4 303s in the first cannon armed versions because the hispano was so temperamental during its long development process with the Spit. Later they didn't need the extra kill power so they paired it with 50 cals to give longer length of fire and lighter weight in the wings.

Mixed gun packages are a bad solution, but the weight of fire was required so that solution was used until better could be taken advantage off.

[NZTyphoon]

The British started using an armament mix of 2 x .50 Brownings and 2 x 20mm Hispanos in their Spitfire IXs, starting in March 1944. There were two problems with the .303 machine guns mounted in the outer wings; a major one was that as the outer wings flexed slightly the .303 bullets tended to spread out in a cone; spot harmonisation helped but didn't cure the problem - plus the 303s were relatively ineffective against even lightly armoured targets and the British wanted to use their Spitfires to support ground troops as part of the Second Tactical Air Force.

So, on the Mark IXs, the 20 mm Hispano cannon were moved outboard and .50 cal M2/AN with 250 rpg was added to the inner gun-bay. From Wikipedia: http://en.wikipedia.org/wiki/Supermarine_Spitfire_%28late_Merlin_powered_variants%29#cite_note-Shores_and_Thomas_2008.2C_pp.586.2C_607.-6 "The first trial installation of the installation (modification 1029) was made in BS118 in November 1943; by mid-March 1944 the first Spitfires to be modified were from 485(NZ), 222 and 349 Squadrons. Spitfires with this armament were referred to as Spifire IX LF .5 and the "E" suffix was not officially introduced until early 1945. This armament was standard for all Spitfire Mk IXs and XVIs used by the 2nd Tactical Air Force as fighters and fighter-bombers from shortly after D-Day. (Christopher Shores and Chris Thomas "2nd Tactical Air Force Volume four; Squadrons, Camouflage and Markings, Weapons and Tactics 1943-1945" 2008, 586 and 607)"

[Bino]

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.

The guns in the FW-190 variants evolved over time.  Also, the Luftwaffe found they needed more firepower to bring down the big Allied four-engined bombers.

FW-190A-1
    nose = 2 x 7.9 mm MG17 machine-guns
    wing root = 2 x 7.9 mm MG17 machine-guns
    wing outboard = 2 x 20mm MG/FF cannon

FW-109A-2
    nose = 2 x 7.9 mm MG17 machine-guns
    wing root = 2 x 20mm MG-151/20 cannon
    wing outboard = 2 x 20mm MG/FF cannon

FW-190A-6
    nose = 2 x 7.9 mm MG17 machine-guns
    wing root = 2 x 20mm MG-151/20 cannon
    wing outboard = 2 x 20mm MG-151/20 cannon

FW-190A-7
    nose = 2 x 13 mm MG131 machine-guns
    wing root = 2 x 20mm MG-151/20 cannon
    wing outboard = 2 x 20mm MG-151/20 cannon

[Tank-Ace]

Well......

Germany started out with the 7.92mm and some of the 20mm MG/FF. The 7.92mm was found to be ineffective, and the MG/FF was found to be less than idealy designed. And so they switch to the MG/FF-M as the main armament, as 7.92's stuck on the frame where there was space.

Later, you've got the 15mm Mg151/15, as an upgrade to the 7.92mm, skipping over the heavy MG entirely. Not really a good fit for the cowl, and so they swap it out with the MG/FF-M's. Howver, the Mg151 is found a bit wanting, and so its upgraded to the 20mm Mg 151/20.

After its evident that the 7.92's have pretty much reached the end of their usefull liftime as aircraft armament, they upgrade to the 13mm Mg 131. The wings and hub cannon spots are already carrying weapons more effective than the 13mm, so they just use them as cowl guns.

As they are facing more and more bombers, they upgrade further to the 30mm Mk 103 and later the Mk 108.



For the spits and hurricanes, its because they started out with .303's, which were found to be ineffective. The UK just skipped past the HMG's, and went right to the 20mm as the main armament, backed up by 4 .303's, which were still a respectable secondary armament, even if they could have been better layed out.

Later, they upgraded the 4 .303's to the US-built .50 caliber as secondary armament, and stuck with the 20mm as the main armament.


For the USA, they started with LMG's chambered for 30-06, and some fighters with the .50cal M2 as the main armament, backed up by the .30 cal. As the .30 cal became more and more ineffective (although still a relative term aganinst the Japanese aircraft), they upgraded to the .50cal as the standard amament, and just slapped more guns on in place of using cannons.

The P-38, P-39, and early P-51 were where they exiramented with the 20mm and 37mm. The .50 cal was a better general purpose gun, and so was kept on as the main armament even for the Saber.




Look at it this way: you want to have firepower, but you also want to keep weight to a minimum. These are two conflicting goals. And so you use what is most effective for its weight.

[NZTyphoon]

Not forgetting the British adopted four 20mms for all of its later single seat and single engined fighters ie; Hurricane IIc, Typhoon IB, Tempests, Meteors, Spitfire 21-24, Seafire 45-47, Fireflys, Fury/Sea Fury, Vampires, Hornets - most of them adopting the lighter, shorter Hispano V - there was no longer the complication of having to supply ordnance and spares for two types of weapon, and the higher rof of the Mk V made up for any penalty in muzzle velocity. The Americans had some trouble adopting and adapting the Hispano as the M1 and only used four 20mms as the primary armament in the P-61 and, post-war, the F7F and F8F-2 and F4U-4Bs through to the AU-1.