The WWII Fighter Gun Debate

[Mario]

http://users.skynet.be/Emmanuel.Gustin/fgun/fgun-in.html

[Don Phillipson]

Post by Mario
http://users.skynet.be/Emmanuel.Gustin/fgun/fgun-in.html

This web page obscures rather than clarifies the two technicl
changes of the WW2 period.

#1 = Calibre. WW1 machine guns were of current infantry
rifle calibre ("small bore" as specified in the 1890s, approx.
0.30 inch.) By the 1930s heavier machine guns were
available, typically 0.50 inch, and US military aviation
adopted the half-inch MG. By contrast, German and
British military aviation stuck with the small bore (0.30")
because conversion to half-inch would produce fewer
weapons (and cost more in resources.)

#2 = Explosive shells, fired by "cannons" as distincf from
MGs firing solid shot. German fighter aircraft were equipped
with cannon from 1939 but the RAF did not deploy them until
1941. Cannons and their ammunition are of course heavier
than MGs, so each aircraft can carry fewer rounds. This was
why BF 109 and FW 180 were armed with both cannon and MG.

Explosive shells cause more damage than solid shot
(and half-inch bullets cause more damage than 0.30" rounds.)
Planners knew this but in both cases 1 and 2 attempted to
consider "the big picture," reckoning quantity as well as
quality -- which was why the RAF, USAAF and Luftwaffe
were differently armed.

[John Dallman]

Post by Don Phillipson
British military aviation stuck with the small bore (0.30")
because conversion to half-inch would produce fewer
weapons (and cost more in resources.)

The British had done tests in the 1930s and reached the conclusion that
many small-calibre hits did more damage than the fewer larger calibre
hits that would come from the same weight of larger calibre machine guns.
This may have been correct at the time, but it was made obsolete as
aircraft became more strongly constructed.

They had decided on 20mm as the next gun after .303, and actually managed
that. The US tried to go 20mm, but never got it to work well until after
the war, for reasons that don't seem entirely clear.

John

[Bill Shatzer]

Post by John Dallman

Post by Don Phillipson
British military aviation stuck with the small bore (0.30")
because conversion to half-inch would produce fewer
weapons (and cost more in resources.)

The British had done tests in the 1930s and reached the conclusion that
many small-calibre hits did more damage than the fewer larger calibre
hits that would come from the same weight of larger calibre machine guns.
This may have been correct at the time, but it was made obsolete as
aircraft became more strongly constructed.
They had decided on 20mm as the next gun after .303, and actually managed
that.

I believe the Spitfire Mk.IX and Mk.XIV with the 'E' wings supplemented
the 20mm cannon with two Browning .50 caliber MGs in lieu of the four
.303 caliber MGs used on earlier marks.

Post by John Dallman
The US tried to go 20mm, but never got it to work well until after
the war, for reasons that don't seem entirely clear.

The US Navy used some number of a/c equipped with 20mm cannon -
including the entire SB4C run and more modest numbers of F6F-5s and F4U-1Cs.

That the 20mm option was not pursued more vigorously was not because of
any particular problems with the 20 mm cannon but rather because the
generally light construction and lack of armor and self-sealing gas
tanks on most Japanese aircraft made the .50 caliber weapons "good
enough" to handle most Japanese aircraft with which they met in combat.

[John Dallman]

Post by Bill Shatzer
I believe the Spitfire Mk.IX and Mk.XIV with the 'E' wings
supplemented the 20mm cannon with two Browning .50 caliber MGs in
lieu of the four .303 caliber MGs used on earlier marks.

They did. That was an expedient step, rather than part of a long-term
plan.

John

[William Clodius]

<snip>
The US Navy used some number of a/c equipped with 20mm cannon -
including the entire SB4C run and more modest numbers of F6F-5s and F4U-1Cs.
That the 20mm option was not pursued more vigorously was not because of
any particular problems with the 20 mm cannon but rather because the
generally light construction and lack of armor and self-sealing gas
tanks on most Japanese aircraft made the .50 caliber weapons "good
enough" to handle most Japanese aircraft with which they met in combat.

However the USAAF was a bit larger than the USNAF and faced the Germans
and Italians as well as the Japanese. These opponentt oft had self
sealing gas tanks and significant armor, but the USAAF fielded an even
smaller percentat of cannons on theri aircraft.

[Scott M. Kozel]

Post by Bill Shatzer
That the 20mm option was not pursued more vigorously was not because of
any particular problems with the 20 mm cannon but rather because the
generally light construction and lack of armor and self-sealing gas
tanks on most Japanese aircraft made the .50 caliber weapons "good
enough" to handle most Japanese aircraft with which they met in combat.

In the case of Europe, the USAAF's German opponents were light and heavy fighters, where the .50 calibers were sufficient to destroy them.

[Diogenes]

On Tue, 14 Jun 2016 14:41:34 -0400, "Don Phillipson"

Post by Don Phillipson

Post by Mario
http://users.skynet.be/Emmanuel.Gustin/fgun/fgun-in.html

This web page obscures rather than clarifies the two technicl
changes of the WW2 period.
#1 = Calibre. WW1 machine guns were of current infantry
rifle calibre ("small bore" as specified in the 1890s, approx.
0.30 inch.) By the 1930s heavier machine guns were
available, typically 0.50 inch, and US military aviation
adopted the half-inch MG. By contrast, German and
British military aviation stuck with the small bore (0.30")
because conversion to half-inch would produce fewer
weapons (and cost more in resources.)
#2 = Explosive shells, fired by "cannons" as distincf from
MGs firing solid shot. German fighter aircraft were equipped
with cannon from 1939 but the RAF did not deploy them until
1941. Cannons and their ammunition are of course heavier
than MGs, so each aircraft can carry fewer rounds. This was
why BF 109 and FW 180 were armed with both cannon and MG.
Explosive shells cause more damage than solid shot
(and half-inch bullets cause more damage than 0.30" rounds.)
Planners knew this but in both cases 1 and 2 attempted to
consider "the big picture," reckoning quantity as well as
quality -- which was why the RAF, USAAF and Luftwaffe
were differently armed.

Choosing an armament platform for a fighter aircraft involves, like
every anydecision, compromises

On one hand you can go with a large number of small calibre guns with
a high rate of fire and a rather large ammo storage (e.g., the 8 gun
Spitfire and Hurricane). The AN/M2 aircraft version of the U.S.
Browning machine gun in .30-06 calibre had a cyciical rate of fire of
1,350 rounds per minute. The Brits used the same gun in .303, which
probably had a similar rate of fire..So an 8 gun aircraft could put
out 180 rounds per second of thirty calibre fire. This is an advantage
in fighter-to-fighter combat when time frames are short and the pilot
will only be in a firing position of a few seconds.

At the other end of the spectrum is the small number of heavy calibre
guns (20mm or larger) with a lower rate of fire and smaller ammo
storage. The Hispano 20mm had a rate of fire between 600 and 800 rpm,
depending on model. So a 4x20mm fighter could generate between 40 and
56 rounds per second. A cannon would be better for engaging bombers,
since the firing time frame would be longer and the explosive shells
more effective.

The U.S. fighters used the Browning AN/M3 .50 calibre gun which cycled
at 1,200 rpm, so a USAAF or USN six gun aircraft would fire at the
rate of 120 rounds per second (or in the case of the P-47, 160 rps.)
This was a good balance of rate of fire versus striking power, and the
F-86 Sabre jet used the same armament during the Korean War.

However the U.S. did intend to go to 20mm during WWII, but had
reliability problems with their version Hispano cannon.

At the further end of the "big cannon" fighters were the bomber
interceptors that the Luftwaffe sent up to attack the Allied bombers.
Some variants of the FW-190 and Me-09 carried as many as 6 20mm
cannon, sometimes in conjunction with a 30mm cannon. They were
effective against the bombers, but the heavy weight of the cannon
reduced maneuverability and made them vulnerable to Allied escort
fighters.The Me-262 jet fighter had 4x30mm guns, but was too little
and too late to counter the Allied aerial offensive.

----
Diogenes

The wars are long, the peace is frail
The madmen come again . . . .

[Geoffrey Sinclair]

Post by Mario
http://users.skynet.be/Emmanuel.Gustin/fgun/fgun-in.html

As noted it is a moving target.

Before talking about the guns consider the gun sights,
none to ring and bead to reflector to gyro to just radar
range finding to automatic (computer) sights with their
improvements in accuracy.

The more accurate the sights are the more useful it
is to up the rate of fire. Also the higher the speeds
involved the greater the need for higher rates of fire.
Speed also pushes you towards higher muzzle
velocities.

Next consider airframe strength, the stronger it is the
more destructive power required, which pushes you
towards explosive filled shells. In WWII terms would
the average US fighter have stayed with the historical
armament if they were required to defeat B-17/24/29
raids? Note the cannon armament of the USAAF
night fighter, the P-61

At the start of WWII there were still fabric covered
airframes in use as military aircraft, in addition most
fuel tanks were not self sealing and little armour was
carried That meant rifle calibre machine guns were
adequate, for example the analysis of the early Battle
of Britain fighting indicates the 8 rifle calibre machine
gun armament of the RAF fighters was more lethal than
the 2 rifle calibre machine gun, two 20 mm cannon
armament of the Bf109. In addition the fusing of the
Bf109 cannon shells was too quick, which favoured the
Spitfire surviving more than the Hurricane with its fabric
covered fuselage and one fuel tank not self sealing.

At the other end of the war the USN undertook a hasty
upgrade of its ship board AA armament with the kamikaze
threat, the until then satisfactory 20mm guns were too light,
the 40mm was needed, to not just shoot down the attacker
but blow it to pieces, prevent it going ballistic.

In between there all sort of permutations depending on
the expected mission. The P-39 and P-63 had a 37 mm
cannon, the RAF bomber destroyers the Whirlwind (from
1938) and Beaufighter (from 1939) carried four 20 mm
cannon, versus the 8 machine guns of the standard day
fighters.

In 1941 the RAF survey of units found those expecting to
meet fighters wanted the rifle calibre machine guns, those
that expected to meet bombers wanted the cannon. In the
meantime Hawker built the 12 rifle calibre machine gun
Hurricane mark IIB from February 1941 to November 1942
and the four cannon mark IIC from March 1941 to end of
Hurricane production in July 1944.

There seems little doubt the RAF would have liked to
retire the rifle calibre machine guns probably from mid
war, in both fighters and bombers. Supply problems
prevented this, while the Spitfire gun heating meant it
could not normally carry the mid war RAF standard
fighter armament of four 20mm cannon, until the
redesigned wing of the mark 21 or later.

The Fw190A started with four rifle calibre machine guns,
then 2 machine guns and two 20 mm cannon, then 2
machine guns, 2 high velocity and 2 low velocity 20 mm
cannon and finally ended up with 2 heavy machine guns
and four high velocity 20 mm cannon, ignoring the special
bomber destroyers. The Fw190D dropped 2 of the cannon
as it was seen more for fighter versus fighter combat.
The Ta152C derivative of the design had more room in the
forward fuselage so it had 2 fuselage mounted 20 mm
cannon plus 2 in the inner wings plus a 30 mm motor
cannon.

And as is known the Germans did major firepower upgrades
to deal with the IL-2 and allied four engined bombers, heavy
machine guns in place of rifle calibre, more 20 mm cannon
as well as replacing 20 mm with 30 mm and so reducing
the number of hits to shoot down a heavy bomber from around
20 or so to 1 to 3.

The USN started with four heavy machine guns in the F4F,
then found the pilots disliked the 6 gun installation with its
more limited ammunition supply per gun. It switched to 6
heavy machine guns in the F6F-3 then to two 20 mm cannon
and 4 heavy machine guns in the F6F-5 from April 1944.
A limited run of 200 F4U-1 with four 20 mm cannon replacing
the standard 6 heavy machine guns was undertaken between
August 1944 and January 1945 and it is believed a similar
run of F4U-4 was done in early 1945. While the cannon
armament became standard in the F4U-4B from April 1946.

The 1944 twin engined F7F carried radar, four heavy machine
guns and four 20 mm cannon.

The lightweight F8F-1 interceptor carried four heavy machine
guns when production started in February 1945, with smaller
numbers of four cannon F8F-1B from December 1945, from
September 1947 the cannon armament was standard.

Meantime the USAAF fighters, the F-80, 82, 84 and 87, stayed
with the heavy machine gun

It would seem the four high velocity 30 mm cannon in the Hawker
Hunter was considered to be overkill.

So my take is, what is the target, how fast is it, how strong is it,
how much damage do you need to inflict, how accurate are
the sights on average and what is considered an adequate
firing time. Then the armament choice should be clear.

Or as James Lacey is reported to have said when queried
about the fact he claimed a shot down a Japanese aircraft only
using 9 rounds of cannon, "Oh really flight, as many as 9, you
surprise me". See also David McCampbell's use of his F6F's
ammunition.

Geoffrey Sinclair
Remove the nb for email.

[JL McClellan]

A number of articles from 1941-1944 discuss this matter as seen by
contemporary writers can be found on the page
http://www.legendsintheirowntime.com/LiTOT/Content/Articles/weapons.html

Start about halfway down the page in the "Guns, Gunners and Turrets"
section. Included are articles by Peter Masefield introducing his metrics
of pounds per minute and muzzle horsepower.

Post by Mario
http://users.skynet.be/Emmanuel.Gustin/fgun/fgun-in.html