CANNON OR MACHINE GUN? Pt. 1

[Jank]

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.

 

[MacArther]

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**

 

[Aggie08]

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.

 

[Jank]

I stand corrected.

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

 

[Erich]

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

 

[Glider]

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.

 

[Twitch]

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.

 

[Glider]

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.

 

[Barrett]

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.

 

[Barrett]

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?"

 

[Barrett]

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.

 

[P-39 Expert]

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.

 

[Glider]

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

 

[swampyankee]

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.)

 

[Shortround6]

(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.

 

[Glider]

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.

 

[Shortround6]

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.

 

[swampyankee]

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.

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.

 

[MIflyer]

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.

 

[varsity07840]

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.