# CANNON OR MACHINE GUN? Pt. 1



## syscom3 (Apr 7, 2006)

I received this in an e-mail today.

CANNON OR MACHINE GUN? The Second World War Aircraft Gun Controversy

Anthony G Williams

This article first appeared in Aeroplane Magazine in
September 2004. It is based on material in 

Flying Guns – World War 2: Development of Aircraft
Guns, Ammunition and Installations 1933-45



The Second World War stimulated an important advance
in aircraft gun armament. The fighters of most
combatant nations began the war with a few
rifle*calibre machine-guns (RCMGs) of 7.5-8 mm
calibre, but, by the end of the conflict, cannon of 20
mm or greater calibre were standard. The one exception
was the USA, which relied overwhelmingly on the 12.7
mm (0.50 inch) M2 Browning heavy machine-gun (HMG).
Students of armament history continue to argue: why
did this happen, and were the Americans right?



EARLY FIGHTING

In 1939 the RAF's new Spitfire and Hurricane fighters
were remarkable for their heavy battery of eight
wing-mounted 0.303 inch (7.7 mm) RCMGs; twice as
powerful as that of any other major fighter. In
contrast, Germany's Luftwaffe had been watching the
French use of engine-mounted cannon. In 1932 this
resulted in a requirement for a fighter with two RCMGs
or a single 20 mm cannon. The weapon considered was
the large, very powerful but slow-firing
Rheinmetall*Borsig MG C/30L, firing through the
propeller hub. An initial experiment with a prototype
Heinkel He 112 in the Spanish Civil War showed that
this installation was unsatisfactory for aerial
combat, though effective in ground attack.

Germany then went to the opposite extreme and selected
the small, low-velocity Swiss Oerlikon FF 20 mm cannon
for development. A modified version, the MG-FF, was
put into pro*duction by Ikaria Werke Berlin, and
entered Luftwaffe service. Initial attempts to fit
this as an engine gun ran into reliability problems,
so the Messerschmitt Bf 109E-3 of 1939 carried two
MG-FFs in the wings and a pair of 7.92 mm MG 17 guns
synchronised to fire through the propeller disc.
However, many Bf 109s were still armed with four RCMGs
at the start of the war.

The Battle of France caught the French with few
fighters capable of dealing with the Bf 109s. Most
French fighters carried a mixture of 20 mm cannon and
RCMGs; the best was the Dewoitine D.520 with its four
wing-mounted 7.5 mm MAC34 M39 MGs and the powerful,
fast-firing Hispano-Suiza HS 404 moteur canon. The
US-*built Curtiss Hawk H-75A, with four or six 7.5 mm
FN-Browning guns, was too lightly armed.

One lesson of early fighting was that the RAF
fighters' battery of RCMGs was less effective than
expected. Although the eight guns between them fired
no fewer than 160 rounds per second (rps), they were
initially adjusted to concentrate their fire at the
long range of 365 m which led to the bullet strikes
being spread across the target at shorter ranges. As
self-sealing fuel tanks and armour became much more
common during 1940, it proved necessary to concentrate
fire at much closer ranges.

The problem was that the small bullets fired by the
RCMGs could not carry enough incendiary or explosive
to guarantee success, and also had insufficient
penetration to defeat armour reliably. A series of
ground tests carried out by the British, firing at a
redundant Bristol Blenheim from 180 m to the rear with
various British and German guns and ammunition,
revealed that the .303 incendiary B Mk VI bullets
would set light to a Blenheim wing tank with only one
hit in five; during the Battle only one or two of the
eight guns were normally loaded with this ammunition.
Other .303 and 7.92 mm incendiaries were only half as
effective. Similarly, while both German and British
steel-cored armour-piercing (AP) rounds could
penetrate up to 12 mm of armour plate if fired
directly at it from 180 m, most of the bullets were
deflected or tumbled by first passing through the
fuselage skin or structure. In consequence, only a
quarter to a third of the bullets reached the
Blenheim's 4 mm-thick armour plate at all, and very
few penetrated it.

The Luftwaffe relied more on their 20 mm MG*FF cannon,
which had some interesting advantages and
disadvantages. The guns were more than twice as heavy
as the 7.92 mm MG 17 and fired only half as fast, at
about 9 rps. The muzzle velocity was also lower,
giving a different trajectory and time-to-target.
Moreover, the 60*round capacity of its drum magazine
limited the weapon to only about 7 secs of firing.
However, the big shells weighed about 12 times as much
as the RCMG bullets, and their high-explosive filling
caused blast damage, as well as throwing high-velocity
shell fragments around.

In May 1940 the Bf 109E-4 entered service with the
modified MG-FFM gun, adapted to fire the new
Minengeschoss (mine shell) ammunition which had very
thin walls and a doubled capacity for high explosive
(HE) and/or incendiary. As a bonus the shells were
lighter, permitting a higher muzzle velocity. The
theory was that solid bullets or AP cannon shells
relied on hitting the relatively small vital areas to
have an effect, whereas an HE shell could cause
serious damage regardless of where it struck. There is
no doubt that this theory was correct: the Spitfires
and Hurricanes would have had far more effect on the
Luftwaffe's bombers had they been armed with four
MG-FFM cannon, which would have weighed little more
than their battery of RCMGs..


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## syscom3 (Apr 7, 2006)

CANNON OR MACHINE GUN? The Second World War Aircraft Gun Controversy

Anthony G Williams

This article first appeared in Aeroplane Magazine in
September 2004. It is based on material in 

Flying Guns – World War 2: Development of Aircraft
Guns, Ammunition and Installations 1933-45
THE SEARCH FOR BIGGER GUNS

The RAF had realised years before the war that the
.303 MG might become inadequate as a primary aircraft
gun, given the steady increase in speed, strength and
toughness of aircraft. They considered, but rejected,
.50 inch (I2.7 mm) guns as giving insufficient
advantage over the .303. Instead, they sought a good
20 mm cannon, which they thought would be far more
effective due to its explosive ammunition, and found
one in the new French Hispano-Suiza HS.404. This was
selected in the late 1930s, and specifications were
written for a new fighter to carry it (the Westland
Whirlwind), but problems in setting up UK factories
meant that only a few guns were available for the
Battle of Britain.

To save time the Hispano was fitted to existing
single-engined fighters for testing, and a squadron of
Spitfire IBs saw service during the Battle. However,
the gun was designed to be mounted on a massive engine
block, and did not like being installed in a far more
flexible wing. Moreover, the initial installation had
the guns on their sides to bury the big drum magazines
in the wings, and the Hispano did not like this at
all. The result was such appalling unreliability, the
guns frequently jamming after only one shot, that the
squadron requested its old aeroplanes back.

Throughout the Hispano's life, fine-tuning of
installations was required to make it reliable in wing
mountings. Guns mounted in the much more rigid
fuselages of such aircraft as the Whirlwind,
Beaufighter and Mosquito caused far fewer problems.
Once working properly, the big cannon was a formidable
weapon. Compared with the MG-FF it was slightly
faster-firing at 10 rps, and its much bigger cartridge
cases generated a considerably higher muzzle velocity,
which improved both hit probability and penetration.
While the Allies never introduced the Minengeschoss
technology, so their shells only carried half the
HE/Incendiary (HEI) load, the heavy Hispano shells'
better penetration meant they could inflict
considerable damage. The Hispano soon changed from a
60-round drum magazine to a belt feed giving much
greater ammunition capacity (which the MG-FF never
had, other than in an obscure nightfighter
installation). The penalty was that the Hispano was
almost twice as long as and double the weight of the
German gun; unwelcome features for wing-mounted
weapons.

RAF fighters carried a mixture of HE or HEI and plain
steel "ball" (practice) rounds (which had good
penetration) until the emergence of the semi-armour
piercing incendiary (SAPI) in 1942, after which the
standard loading was 50/50 HEI and SAPI. The German
cannon were not exclusively loaded with Minengeschoss,
but used them mixed with older-type HEI-T shells
(retained because, unlike the M-Geschoss, they could
carry a tracer) and later some API rounds as well, in
varying proportions.

The Germans were not satisfied with the MG-FFM, which
had been adopted as an interim measure pending the
development of a purpose-designed cannon. This duly
emerged as the Mauser MG 151, which gradually took
over from 1941. Initially, the Mauser had been
designed to use a high-velocity 15 mm cartridge, but
it saw relatively little service in this form. Wartime
experience led to the cartridge case being modified to
accept the 20 mm shells from the MG-FFM, surrendering
muzzle velocity and penetration in the interests of
far greater destructive effect. The 15 mm version was
available with HE shells, but they were considered too
small. The resulting MG 151/20 was intermediate in
size, weight and muzzle velocity between the MG-FFM
and the Hispano, but was faster-firing at 12 rps. It
was a superb design which the Americans tried to copy,
producing some 300 guns in .60 inch (15.2 mm) calibre,
designated T17, but they never adopted it.

Later in the war, various new German guns emerged with
calibres of up to 50 mm. The most significant ones
were the Rheinmetall-Borsig MG 131, MK 103 and MK 108.
The MG 131 was a 13 mm HMG intended to replace the
RCMGs in both fixed and movable mountings, and
therefore kept as small and light as possible, making
it the least powerful HMG to see service. The other
guns were both in 30 mm calibre but otherwise very
different. The MK 103 was a huge, high-velocity
slow-firing gun, while the MK 108 fired much smaller,
low-velocity cartridges at a very creditable 10 rps,
and was only half the size and weight. Their use was
really prompted by the difficulty the Luftwaffe was
experiencing in shooting down USAAF B-17 bombers.
Their 30 mm M-Geschoss HEI shells were highly
effective, containing four times as much HE as the 20
mm version, and three or four hits with these could
bring down a bomber, compared with 20 hits with 20 mm
ammunition.

In 1941 the USSR was attacked by Germany and thereby
drawn into the wider conflict. As well as the
very-fast-firing (30 rps) 7.62 mm ShKAS, it had in
service an excellent HMG, the 12.7 mm Universal
Berezin, and a 20 mm cannon, the ShVAK. The ShVAK had
actually started life as a 12.7 mm gun. It weighed the
same as the MG 151/20 and was slightly faster-firing,
but the ammunition was less effective as the shells
had only a small HE capacity. Towards the end of the
war the Berezin was also altered to fire the same 20
mm ammunition as the ShVAK; at 25 kg the resulting
B-20 was the lightest gun of this calibre to see
service. The Soviet preference was to install all guns
in the fuselage of their little fighters rather than
in the wings, to concentrate firepower and make the
aircraft more agile. Because this limited the number
of guns, a relatively small number of aircraft was
equipped with larger guns as engine cannon, including
the powerful 23 mm VYa-23 and 37 mm NS-37. Because of
the weight, recoil and relatively low rate of fire of
these weapons, these were deemed suitable for expert
pilots only.


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## syscom3 (Apr 7, 2006)

CANNON OR MACHINE GUN? The Second World War Aircraft Gun Controversy

Anthony G Williams

This article first appeared in Aeroplane Magazine in
September 2004. It is based on material in 

Flying Guns – World War 2: Development of Aircraft
Guns, Ammunition and Installations 1933-45

ENTER THE AMERICANS - AND THE JAPANESE

The end of 1941 also saw America and Japan enter the
war. Their aircraft weapons were very different.
America relied almost entirely on the Browning
machine-gun, not just in .50 (12.7 mm) calibre, but,
for the first couple of years, in .30 (7.62mm) as
well. The Japanese army and navy air forces followed
their own paths, the army steadily up-gunning from 7.7
mm through 12.7 mm machine-guns and later 20 mm
cannon, with 30 mm and even larger guns seeing limited
service by the end of the war. The navy started with a
mixture of 7.7mm MGs and Type 99 (Oerlikon) 20 mm
cannon and continued to rely on this cannon (initially
the low-velocity Type 99-1, later the more powerful
Type 99-2), although it did make some use of HMGs and
was also introducing 30 mm guns by the end of the war.
As in Germany, the destruction of American heavy
bombers was a strong incentive for the development of
weapons of 30 mm or larger calibre.

The Americans did not intend to make such a commitment
to the Browning MGs. Both before and during the war
considerable efforts were made to secure alternative
aircraft guns. Trials of foreign equipment resulted in
the selection of the 20 mm Hispano-Suiza HS 404, large
numbers being made. The Browning-designed 37 mm M4
cannon was also introduced, although used almost
exclusively by the Bell P-39 and P-63. However, the
standard fighter armament became a battery of six .50
inch Browning M2 HMGs.

This has led to the often-expressed view that the .50
inch M2 was the best all-round fighter gun of the war.
After all, the USAAF and US Navy fighters
unquestionably came to dominate the skies in which
they fought. If there had been a better gun, America
would have used it. However, the truth is not quite as
simple as that. There are two issues here; how good
was the .50 M2 compared with other HMGs, and how
effective was it compared with cannon?

The most obvious comparator was the Soviet UB, which
fired ammunition of virtually identical power. The UB
weighed 25 kg, compared with the M2's 29 kg, but the
Soviet gun fired at 17.5 rps, compared with around 13
for the M2. In terms of power- to-weight ratio the
Berezin was therefore clearly superior. The Browning
fared better against most other HMGs, as they all
fired less-powerful ammunition, so the M2 enjoyed
advantages in range and penetration. However, it had a
slightly lower rate of fire than the German and
Japanese guns (both around 15 rps), and was also
bigger and heavier. The most powerful of all of the
HMGs was the 15 mm MG 151, but this was heavier and
slower-firing than the M2. Overall, therefore, the .50
M2 was not the best of the HMGs but was about average,
with reasonable performance for its weight.

How did HMGs compare with 20 mm cannon? The first
problem is that the cannon varied hugely in size,
weight and performance. The MG*FFM, Type 99-1 and B-20
were all lighter than the M2, but the first two were
significantly worse in terms of muzzle velocity and
rate of fire, although the B-20 matched the M2's rate
of fire and was not far behind in velocity. The
Japanese Ho-5 and Type 99-2 and the ShVAK and MG
151/20 were all somewhat heavier. Muzzle velocities
and rates of fire were closer to the M2's but
generally still not as good. The Hispano was
significantly heavier and slower-firing until the
British Mk V emerged near the war's end, matching the
MG 151/20 in weight and rate of fire.

The foregoing compares only the guns' efficiency; it
takes no account of ammunition, the area in which the
HMG loses most ground. The 20 mm cannon shells were
not only two to three times heavier than HMG bullets,
but their HEI contents greatly increased their
effectiveness. Although HE ammunition was available
for most HMGs, their small bullets severely limited
the quantity of chemicals carried, so the Americans
decided not to use them. Initially, the M2 used a mix
of incendiary and AP bullets, with some tracers, but
in 1944 the M8 API began to take over. Rather
curiously, this was based on the Soviet B.32 API used
in the Berezin.

It is difficult to assess the effectiveness of
different ammunition types, but various tests suggest
that a typical World War Two-era HE or incendiary
shell, with chemical contents forming about 10 per
cent of total shell weight, was about twice as
destructive as a plain steel shell of similar size and
weight. This makes it clear that 20 mm cannon were
considerably more destructive for a given total weight
of armament than any HMG could hope to be. For
example, the .50 M8 API contained less than one gram
of incendiary, whereas the 20 mm Hispano SAPI achieved
similar armour penetration but carried more than ten
times as much incendiary material.

This advantage was recognised by the US Navy. After
comparing the .50 M2 and the 20 mm Hispano they
estimated that the cannon was three times as
effective. In other words, the typical RAF armament of
four 20 mm cannon was twice as destructive as the
USAAF's six .50 HMGs, for very little more weight.
Proponents of the Browning HMG point to its excellent
ballistics, which enhanced its range and hit
probability. But the Hispano's muzzle velocity was
very similar, and although the blunt-nosed shells were
less aerodynamic the difference over typical
air-combat ranges was not significant.

The cannon's advantages are clearly shown in the
decisions made as a result of combat experience by air
forces with a choice of good HMGs and cannon. We have
already seen how Germany preferred the 20 mm version
of the MG 151 despite its poorer ballistics. In the
12.7 mm Berezin the Soviets had arguably the best HMG
of the war, but they still preferred the heavier,
slower-firing 20 mm ShVAK. Japan had several good HMGs
available; the army's Ho-103, and the navy's 13 mm
Type 3, a .50 Browning chambered for slightly
larger-calibre ammunition, but they made increasing
use of cannon.

So why did the Americans not make more use of cannon,
specifically the 20 mm Hispano they already had in
mass production? There were two main reasons. One was
certainly that the M2 was adequate for its purpose. In
Western Europe the main adversaries were fighters,
which were much easier to damage and shoot down than
bombers. In the Pacific Theatre the Japanese aircraft
were initially poorly protected and easy to shoot
down. Later Japanese aircraft were better protected,
but again these were usually fighters. If the
Americans had faced the need to stop raids by heavy,
well-protected bombers, it is likely that the HMG's
shortcomings would have been starkly revealed.

There was another reason, however, which explains why
the US Navy, despite rating the cannon very highly and
facing the need to deal with attacking bombers and
kamikazes, fitted it to few aircraft. That was serious
production prob*lems with the American Hispano, which
gave it a reputation for unreliability. Despite
production running well into six figures, the American
Hispano failed to achieve an acceptable reliability
standard for the duration of the war.

To return to the original question, were the Americans
right to rely so heavily on the .50 M2 when all other
combatant nations had a clear preference for cannon of
at least 20 mm calibre? The answer has to be yes. It
was adequate for its purpose, and was the only
satisfactory aircraft gun in production in the USA. It
was very reliable (except where the installations
created problems), was made in huge quantities, and
the simplification of supply by comparison with the
diversity of weapons used by the Axis powers gave a
major logistical advantage. However, the Americans
could get away with using a weapon so deficient in
destructive power not only because of the nature of
their opposition, but also because the size and engine
power of their fighters enabled them to carry a
battery of at least six guns, thus making up in
quantity what they lacked in destructive quality.

The advantages of the 20 mm Hispano M2 were not
entirely ignored. It was carried by Lockheed P-38s,
together with four .50 Brownings. It was also
installed in nightfighters, which needed maximum
firepower to convert a short firing opportunity into a
kill. Four were installed in Northrop's P-61 Black
Widow, and two could be mounted in a Grumman F6F-5N.
The cannon's extra firepower was also appreciated for
ground strafing.

After the war the US Navy quickly changed over to the
20 mm cannon in its improved, faster-firing and more
reliable M3 form, but the USAF stayed with the .50 M3
until the fighting in Korea demonstrated once and for
all that the HMG had had its day. From the mid-1950s
the USAF at last replaced the old Browning with 20 mm
cannon, initially the M39 revolver and then the M61
rotary - just as most of the rest of the world was
moving up to 30 mm!


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## Glider (Apr 8, 2006)

This is a good article that I first read in the magazine in question and saved. Its also a good summary of the history re the develoment of aircraft borne weapons


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## lesofprimus (Apr 8, 2006)

Yes it is, good read...


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## Hot Space (Apr 8, 2006)

Yeah, cool that m8 

I would go with a bit of both - 20mm .50's


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## Gnomey (Apr 9, 2006)

Good interesting read syscom.


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## Twitch (Apr 9, 2006)

Setting aside idiosyncrocies of brands of weapons within the same caliber the 20 mm round should have been the acknowledged all around most usefull. The caliber itself seems best suited to the demands of the job in mid to late WW2. While we look at 30 mm types and conclude they are almost specialized in nature as they were mounted on machines in all countries whose role was anti-heavy bomber. On the other end of the spectrum the .30 caliber was about useless except in the very early stages of the war and then mostly in the hands of virtuoso shooters. Those with thirty caliber weapons mostly used them for ranging in their heavier cannon only.

One of the problems with 20 mm magazines was simply that they held too few rounds. 60-100 rounds might have been ample for Saburo Sakai or Adolf Galland who were the products of the cream of the elite best pilots. For the pliots who weren't trained for extended periods due to the need for them to appear in action, it was woefully inadequate.

The .50 caliber weapon of any manufacture had a tradeoff that lessened punch but retained fire time. Frankly it didn't matter if a "good" grade pilot took 700 rounds to bring down an enemy with fifties where an elite pilot used 70 rounds of 20 mms. The good pilot had ample ammo for a couple kills in the magazines even at that poor strike rate. Until much later with somewhat larger mags, 20 mms could not be spread around liberally in the air by trigger-happy pilots.

In later .50s, and 20s ROF was about the same- 740 RPM. The math is easy. You got 200 20mms or 400 .50s. No the 20mm doesn't have exactly twice the killing power to make up for it. It's pretty close but weight and size restrictions make compromise necessary depending on the plane and the ordnance used if we diverge into that area beyond simple caliber cross section alone. All 20 mms are not equal. 12.7/.50s have more parody of universal application.

It's one thing to easily stick a quartet of 20 mm Hispanos inside a Tempest's wing and quite another to get four MG 151s in a Bf 109's. Even if it were possible what about room for ammo?

The pre and early war rifle caliber mentality for aerial weaponry was a throwback to WW I as was the bolt action arm for soldiers- inadequate for the modern combat that was about to unfold. 

The contention of low velocity of early 20 mm weapons is superfluous since the pilots knew their weapons and compensated to whatever degree was necessary. Any halfway sharp aerial gunman could alternate between high and lower velocity weapons by selecting their different triggers then mentally and physically compensate lead, drop and deflection. This was primary stuff. We idiot savants who know all the statistics of all the planes and weapons haven't got a clue to aerial gunnery beyond flight sims.

.50 calibers were acceptable but becoming inadequate by late 1944 were as 20 mms had improved in velocity to the point of being the ideal caliber for times. Even so few planes carried a lot of rounds per gun. 20s should be considered the prime caliber of the aerial war as most effective I believe.

Reactions: Agree Agree:
1 | Like List reactions


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## R988 (Apr 10, 2006)

Nice article I pretty much agree with all it says. 
This is also a very interesting article on the background of the 20mm and the differences between the British and Americans on the subject.
http://www.quarry.nildram.co.uk/US404.htm

This is also great reference site for info and data on WW2 fighter armament
http://www.geocities.com/CapeCanaveral/Hangar/8217/fgun/fgun-in.html


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## syscom3 (Apr 10, 2006)

When it came to strafing, .50's were in some instances more effective than 20mm. 

.50's were just as deadly as 20mm against thin skinned vehicles. Plus, when you need to "hose down" an area with no specific target readily seen, the more lead you have flying around, the higher the probablity you will hit something.


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## Jabberwocky (Apr 10, 2006)

I agree with your general thrust, but have to disagree on some specifics. 




Twitch said:


> One of the problems with 20 mm magazines was simply that they held too few rounds. 60-100 rounds might have been ample for Saburo Sakai or Adolf Galland who were the products of the cream of the elite best pilots. For the pliots who weren't trained for extended periods due to the need for them to appear in action, it was woefully inadequate.



Most 20mm armed fighters actually had between 120 and 150 rpg, some upwards of 200 rpg.

Just looking at the ammunition for single engined fighter with 20mms and their firing time

Spitfire Vb: 60 rpg (6 sec)
Spitfire Vc: 120 rpg (12 sec)
Spitfire IXe: 140 rpg (14 sec)
Spitfire XXI: 150 rpg (15 sec)
Hurricane IIc: 96 rpg (9 1/2 sec)
Typhoon: 140 rpg (14 sec)
Tempest: 200 rpg (16 sec)
Firefly: 160 rpg (16 sec)
109F/G: 150 rpg (12 1/2 sec)
190A3-5: inner 200 rpg ( 16 1/2sec)
outer 55 rpg ( 7 sec)
190A6-9: inner 250 rpg ( 21 sec)
outer 140 rpg ( 12 sec)
A6M1-3: 60 rpg (7 1/2 sec)
A6M5-8: 100 rpg (12 1/2 sec)
Ki-61: 120 rpg ( 8 1/2 sec)
Ki-100: 120 rpg ( 8 1/2 sec)
Ki-84: 150 rpg (12 1/2 sec)
N1K2-J: inner 230 rpg (17 1/2 sec)
outer 150 rpg (11 1/2 sec)
LaGG-1/3: 120 rpg (9 1/2 sec)
La-5/7: 200 rpg (15 1/2 sec)
Yak-1: 120 rpg (9 1/2 sec)
P-38: 150 rpg (15 sec)

With the exception of the Hurricane, early Zeros and early Spitfire Vb, most fighters carried more than 100 rpg for their cannon.



> The .50 caliber weapon of any manufacture had a tradeoff that lessened punch but retained fire time. Frankly it didn't matter if a "good" grade pilot took 700 rounds to bring down an enemy with fifties where an elite pilot used 70 rounds of 20 mms. The good pilot had ample ammo for a couple kills in the magazines even at that poor strike rate. Until much later with somewhat larger mags, 20 mms could not be spread around liberally in the air by trigger-happy pilots.
> 
> In later .50s, and 20s ROF was about the same- 740 RPM. The math is easy. You got 200 20mms or 400 .50s. No the 20mm doesn't have exactly twice the killing power to make up for it. It's pretty close but weight and size restrictions make compromise necessary depending on the plane and the ordnance used if we diverge into that area beyond simple caliber cross section alone. All 20 mms are not equal. 12.7/.50s have more parody of universal application.



Most assesments put 20mm cannon at around 2.5-4 times more powerful than any single .50 calibre weapon. This is generally because of their capacity to carry far larger amounts of HE, while maintaining a relatively high RoF. In terms of power round for round, 20mm rounds are generally assesed as 3-4 times more destructive than their 12.7mm counterparts. 

So, while most 20mm armed fighters don't carry around the quantity of ammunition that .50 armed fighters do, they tend to get more 'bang for their buck', so to speak. For example, the 120 rpg loadout on most Spitfires was the equavilent to a total of around 800-1100 rounds of .50 calibre ammunition, depending on how you measure the effectiveness. More destruction, for less weight and less time on target.

The homogenous .50cal armament was really only used by the USA, and that was primarily a function of them not having an effective alternate. Most nations went to the 20mm as their primary fighter armament, with either RCMGs or HMGs providing back up.


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## lesofprimus (Apr 10, 2006)

I prefer 20mm cannon as well, although 8 x .50's for strafing is just insane.....


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## syscom3 (Apr 10, 2006)

Les, imagine a B25 or A26 gunship coming at you with a dozen .50's.


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## lesofprimus (Apr 10, 2006)

Trust me, I have, and talked to guys who held the trigger down... Insane damage...


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## Glider (Apr 11, 2006)

Or the good old Beaufighter. Working on the three 0.5 = one 20 principle 

4 x 20 and 4 x 0.5 = 16 x 0.5. No wonder it was called the whispering death


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## R988 (Apr 11, 2006)

Glider said:


> Or the good old Beaufighter. Working on the three 0.5 = one 20 principle
> 
> 4 x 20 and 4 x 0.5 = 16 x 0.5. No wonder it was called the whispering death



add in some rockets for good measure as well....


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## Jabberwocky (Apr 11, 2006)

Only Aussie built Beaufighters had 4 x .50 and 4 x 20mm. Most of the British built ones had 6 x .303 (two in the left wing and four in the right) and 4 x 20mm. Less weight of fire and penetration, than with the .50s, but more actual rounds zinging around the place. 6 .303s would put out about 7,200 rounds per minute. In a 2 second firing run a Beaufighter would put out around 240 .303 rounds punctuated with 80 20mm rounds, for a grand total of about 13kg of lead.

The P-61 and F7F were just as scary though, both hauled around 4 x .50 and 4 x 20mms. In a 2 second firing run they would put out about 104 .50 cal rounds and 80 20mm rounds, for a grand total of about 15kg of lead.

Mosquito wasn't far off either with 4 x .303 and 4 x 20mm, with an absolute stack of ammo for both as well.


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## Twitch (Apr 11, 2006)

American pilots liked the 20 mm weapon when they had it. P-38, Spit, and F6F pilots I know were happy with it as they should be. Of course they were mixed with .50 cals. None gave a bucket of spit for .30s no matter how many were mounted. 

I still stand by the statement, "Frankly it didn't matter if a "good" grade pilot took 700 rounds to bring down an enemy with fifties where an elite pilot used 70 rounds of 20 mms." - Because you gotta be good enough to put ordnance on target in the first place, it matters not what caliber gun you got. An "average" skill shooter can simply procure more hits with fifties than with 20s because he's not hording rounds.

Idealy 20/50s would be the perfect armament. You range in and begin damaging with the fifties and touch the cannon trigger to follow up. Repeat as necessary for results. 

It is interesting to note that even cannon-trained air forces like the Luftwaffe continued to mount .30/.50 calibered weapons in addition to cannon. They were there for 2 reasons- to range in and to actually shoot down E/A when cannon shells were gone. Of course almost immediately .30 caliber was obsolete as a killing tool in WW 2. If the half inch caliber wasn't better the Luftwaffe wouldn't have used them on Bf 109s and Fw 190s in place of the .30 cal equivenent- MG 131 vs MG 17.


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## Erich (Apr 11, 2006)

side note :

P-61's in the Pacific only had the 4 .50's installed in the upper turret fitting

ETO P-61 squadrons flet they did not need the .50's as the 4 20mm were enough which they were plus no aerodynamic drag or weight of the upper installation

E


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## Twitch (Apr 11, 2006)

More trivia- In WW II three P-61 gunners each scored five- Lt. Edward Kospel, Lt. Robert Tierney and Lt. Philip Porter.


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## Jank (Apr 11, 2006)

Twitch said, "American pilots liked the 20 mm weapon when they had it. P-38, Spit, and F6F pilots I know were happy with it as they should be. Of course they were mixed with .50 cals."

Don't think so. Which F6F's had a mix of 20mm and .50 cal guns? I don't believe that any F6F's that saw action had 20mm's and am sure that there was no mix of 20mm's and .50's on any of them.


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## MacArther (Apr 11, 2006)

The night fighter variant used the 20mm as a replacement for the two inner most guns on bother wings.

X= 20mm
<>=Plane body
*= 50 cal

**X<>X**


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## Aggie08 (Apr 11, 2006)

I know P-38 pilots very much appreciated their 20mm cannon. I watched a special on the Lightning yesterday and several pilots were amazed at the destruction of just the one cannon. Imagine what just a quick burst of 20mm would do to a jap fighter, and throw in the .50s just for good measure. I'd be impressed.


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## Jank (Apr 11, 2006)

I stand corrected.

http://aeroweb.brooklyn.cuny.edu/database/aircraft/getimage.htm?id=5173


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## Erich (Apr 11, 2006)

actually Tierney and Kospel both scored 6 and they were Radar Ops not gunners.

I was a member of the US night fighters assoc before their dissolvement and have the complet records of the 422nd and 425th nfs

Reactions: Like Like:
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## Glider (Apr 11, 2006)

Jank said:


> I stand corrected.
> 
> http://aeroweb.brooklyn.cuny.edu/database/aircraft/getimage.htm?id=5173



If its any help I believe that the number of Night Fighter versions issued with the 2 x 20 and 4 x HMG were small in proportion because the USA 20 jammed so frequently most of the NF pilots prefered to have the 6 x HMG. 

A number of sources do say that all F6F-5N's were armed with the 20mm's but I don't believe that this is the case. Incidently I believe that many of VMF(N)-514's planes had 6x .50, but with the inner two barrels being extended, which only adds to the confusion because they then looked like 20's.

As an aside all Hellcat F6F-5 had the ability to carry the twin 20s as well as 4 Heavies but as far as I am aware all the day fighters were equiped with the 6 x HMG's.


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## Twitch (Apr 12, 2006)

This should illustrate it. Here's a segment of a book I wrote.

BLACK ‘CAT
Major Bruce Porter in his radar equipped F6F-5N Hellcat night fighter aptly named Black Death, carried four fifty caliber machine guns with 500 RPG outboard and two twenty millimeter cannon inboard with 230 RPG. Something like 1,400 F6F-5Ns were set up this way. This was a potent array that Bruce liked quite well. The Marine had come out the victor three previous times he had met the enemy in battle in his Corsair and was equally as confident of his black F6F.

One indigo night in June 1945 Porter, flying as call sign Topaz One, was informed of a contact by his ground controller, Handyman. The shorter range on-board radar picked up the bogey above him. He dropped the belly tank and firewalled the throttle.

The water-methanol injected Pratt Whitney P-2800-10W put out 2,200 HP and added a fifteen-knot burst of speed in emergencies. Black Death began to close as Handyman vectored him in mile by mile. Patiently following directions yielded Porter a visual. It was a twin-engine Ki-45 “Nick” about 350 feet ahead.

Closing to 300 feet to be certain of perfect gun convergence, Porter held down both triggers rudely interrupting night’s stillness aiming for the right engine and fuselage. The 20s were noticeably slower in firing rate that the .50s. Seventy rounds per second were output by the six heavy guns. Bruce let off of the cannon trigger to save ammo but continued firing the .50s API (armor-piercing incendiary) so as the target would burn and it could be confirmed destroyed. Slugs ravaged the Imperial Army fighter.

“I saw tracers go into the canopy. I doubt if the pilot knew what hit him,” remembers Porter. Two seconds of the devastating fire was all that was needed to send the Nick towards the ocean wrapped in a sheet of flame from nose to tail.

Handyman gave Topaz One another target vector that turned out to be a G4M “Betty” Porter closed near enough to see that an Oka, the piloted rocket powered suicide weapon, was slung beneath the bomber. Bruce knew the Betty had a 20 mm tail gun so he opened up with further delay.

A one to two second burst of machine guns and cannons exploded the bomber and its volatile cargo into a blanket of seething pieces that floated down to the ocean below. This rare double night kill made Bruce Porter an ace.

Black Death had used but 500 rounds of .50 caliber and 200 rounds of 20 mm. Did he like the 20 mm cannon? “Oh yeah, that really gave us some punch,” he told me. Porter’s boyhood marksmen heroes Daniel Boone and Davy Crockett would have been proud.


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## Glider (Apr 13, 2006)

I know that they were set up for the 20's and 50's but I believe that only a minority were actually equipped with the 20's. Certainly the 70 that were given to the RN had 6 x HMG's and if anyone had experience with the 20mm it was the RN.
I have looked for photo's of the NF version and only found one that had the 20's. The look of the 20mm barrel is quite distinctive and very different to the 'normal' barrels of the 6 x HMG.


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## Barrett (May 17, 2018)

Reliability was a b-i-g factor with 20mm weapons among the US WWII pilots I knew. Mostly they were night fighters. Bob Baird, the only USMC night ace, said that functioning problems kept him from using them until his sixth and last kill. That day he test-flew his pet Hellcat five times before he "fired out" a full load on the sixth hop. The other VMFN pilot I knew well was Bruce Porter, CO of 542. He said "The 20s put out a load of lead that was just fantastic when they worked." He made ace on his last encounter, with a rare double (3 previous in Corsairs) but am uncertain whether he used cannon. Jim Swett briefly flew F4U-1Cs with four 20s but I don't recall if he said they featured in any victories. Obviously the allies and axis had different experiences with Hisso-Suiza v. Oerlikon designs. However, I don't recall hearing of much trouble with ship-mounted Oerlikons.


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## Barrett (May 17, 2018)

This just in from a USN guy referring to the trigger times cited in this excellent thread:
"Compared to the F-35B/C, whose podded cannon has just over 3 secs of firing time."
"But who needs a gun any more?"


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## Barrett (May 17, 2018)

Bruce Porter's radar controller, Handyman, was then-Lt. Bill Ballance who became a successful radio host in LA, San Fran and San Diego, where I met him in the 80s. He and Bruce had a live routine based on their recalled transmissions during Bruce's two-victory mission. Bruce died in 09, Bill in 04.


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## P-39 Expert (May 27, 2018)

The 37mm cannon in the P-39 was deemed more reliable than the American 20mm by the Russians.
At 2.3rps it gave 13 seconds of firing time with 30 rounds.
Trajectory was very similar to the synchronized .50MGs out to 400 yards, beyond which you couldn't hit anything anyway.
One strike with a 37mm was normally enough to bring down anything with two engines or less.


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## Glider (May 27, 2018)

That said the US 20mm for aircraft had a shocking reputation for reliability as did its ammnition


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## swampyankee (May 27, 2018)

Glider said:


> I know that they were set up for the 20's and 50's but I believe that only a minority were actually equipped with the 20's. Certainly the 70 that were given to the RN had 6 x HMG's and if anyone had experience with the 20mm it was the RN.
> I have looked for photo's of the NF version and only found one that had the 20's. The look of the 20mm barrel is quite distinctive and very different to the 'normal' barrels of the 6 x HMG.



The UK had experience with both their, UK-built 20 mm and the US-built 20 mm. They found the latter to be unusable for a number of reasons. (Modifications and Attempts at Standardization). They also did not have full control over how aircraft delivered to them would be armed. Since there were relatively few air combats between RN/FAA Hellcats and Axis aircraft, the armament may not have been considered worth a lot of effort to get changed.

The USN considered the 20 mm to be three times as effective as the 0.5 in Browning, but production problems, possibly exacerbated by changes in detail design, reduced its reliability to an unacceptably low value in wing installations until fairly late in the war. 

(note that I'm aware that I'm relying on a single, secondary source for the problems with the US-built 20 mm. On the other hand, it's also evident that the USN was not satisfied with the 0.5 in Browning; I believe that the last USN fighters to use the 0.5 in were the FH-1 Phantom and FJ-1 Fury. The USAF retained the 0.5 in Browning until combat experience in Korea showed it to be inadequate.)


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## Shortround6 (May 27, 2018)

swampyankee said:


> (note that I'm aware that I'm relying on a single, secondary source for the problems with the US-built 20 mm. On the other hand, it's also evident that the USN was not satisfied with the 0.5 in Browning; I believe that the last USN fighters to use the 0.5 in were the FH-1 Phantom and FJ-1 Fury. The USAF retained the 0.5 in Browning until combat experience in Korea showed it to be inadequate.)



I haven't seen any source that claims the US gun was reliable. Plenty of explanations (many somewhat superficial) as to why it was unreliable. 

The whole WW II vs Korea usage gets into real tangled mess as the USAAF was NOT using WW II .50 cal guns (except in left over WW II aircraft Like P-51s) and was NOT using WW II ammo. 
It is even more tangled because the US Navy was not using WW II Hispano guns either, Using something closer to the British MK V hispano (but not the same) 
and shifting to the Colt Mk 12 but not in time to see combat? 
Army used a revolver cannon in the F-86 cannon trials in Korea.


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## Glider (May 27, 2018)

I am afraid that I cannot find the reference but I have seen the report on tests carried out by the US on examples of the 20mm one from each arsenal that manufactured them and the results were very poor.
Re the ammunition, on Malta during the siege they had a run of failures in the air with the 20mm and as you would expect urgently looked into the reasons. They identified that it was a batch of 20mm ammunition from the USA and despite all the desperate shortages, destroyed all the remaining ammunition. This is reported in Spitfires over Malta.


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## Shortround6 (May 27, 2018)

ANd here you hit on a problem faced by the ammo manufacturers in the US.
If the British and US are using different chamber dimensions then which standard is the ammo manufactured to? 
If short enough to fit British chambers it gives light primer strikes in US cannon and failures to fire. If sized to fit US chambers it may prevent the bolt from fully closing and either prevent firing or firing when partially locked. 
Ammo was test fired for reliability at the factory but obviously which gun/s were used as the test guns would affect the ammo that passed the function test.


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## swampyankee (May 27, 2018)

Shortround6 said:


> I haven't seen any source that claims the US gun was reliable. Plenty of explanations (many somewhat superficial) as to why it was unreliable.
> 
> The whole WW II vs Korea usage gets into real tangled mess as the USAAF was NOT using WW II .50 cal guns (except in left over WW II aircraft Like P-51s) and was NOT using WW II ammo.
> It is even more tangled because the US Navy was not using WW II Hispano guns either, Using something closer to the British MK V hispano (but not the same)
> ...



The USAAF/USAF seemed to conclude that the 0.5 in was _nearly_ good enough, and only needed improved ammunition and a greater rate of fire to be adequate for the next decade or so; the USN had concluded that the 0.5 in was not good enough for the future, and should be replaced by the 20 mm. The two services had access* to the same data and came to different conclusions. I think history shows the USAAF/USAF decision to be wrong, and the 0.5 in was inadequate and could not be made so. The USAAF/USAF came to a completely different conclusion from every other air force in the world; one wonders why their conclusion was so much different than all others. I've not heard any explanation that is much more than "the M2 Browning won the war in Europe; nothing else is needed."

----------------------
* Well, one would hope.


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## MIflyer (Jun 6, 2018)

In the book "Kamikazes, Corsairs, and Picket Ships" it says that the 20MM equipped F4U's stationed on Okinawa suffered from unreliability of the guns due to freezing up above 15,000 ft. Supposedly the high altitude tests of the gun had not been accomplished.

In the book "Malta Spitfire Pilot" that I am reading the author complains that the 20MM guns in their Spitfires were of "faulty design." He also said that the Spitfire V's they flew from the USS Wasp to Malta were quipped with both four 20MM guns AND the four machine guns in the outer wings.


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## varsity07840 (Jun 6, 2018)

swampyankee said:


> The USAAF/USAF seemed to conclude that the 0.5 in was _nearly_ good enough, and only needed improved ammunition and a greater rate of fire to be adequate for the next decade or so; the USN had concluded that the 0.5 in was not good enough for the future, and should be replaced by the 20 mm. The two services had access* to the same data and came to different conclusions. I think history shows the USAAF/USAF decision to be wrong, and the 0.5 in was inadequate and could not be made so. The USAAF/USAF came to a completely different conclusion from every other air force in the world; one wonders why their conclusion was so much different than all others. I've not heard any explanation that is much more than "the M2 Browning won the war in Europe; nothing else is needed."
> 
> ----------------------
> * Well, one would hope.


It is notable that the two B-52 tail gun kills in the Vietnam war, during Linebacker II were by quad .50 M3 equipped aircraft.


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