20mm cannon, best, worst, specs, comparison to LMG, HMG etc.

[Greyman]

A post-war British report on the effectiveness of the gyro gunsight shows that the improvement over the regular gunsight greatly depends on the range. The farther out the target is, the greater the improvement. Data from Spitfire combats from October '44 to May '45 showed that at 500 yards, the GGS had a success rate of about 50%, while the GM2 was just over 10%.

The closer the firing was done, the less of an improvement in the GGS was seen.

The results of the two sights crossed at just under 200 yards (just under 70% success rate), and from there the GM2 was slightly superior to the GGS.

 

[Tante Ju]

Very interesting! May you be kind post report? If you have it? I would like to read conclusions. Thank you!

 

[Juha]

Again I agree with Tante Ju, very interesting info, Greyman.
Not very surprising though that at shorther ranges the benefits from GGS diminished, at short range even the chewing gum stuck onto windscreen might be enough.

Juha

 

[P-40K-5]

Hans-Joachim Marseille, master of the deflection shot, use to practice by shooting at the shadow of his aircraft.
in his early career, he was a terrible shot. but lots of practice made him one deadly foe. Its unlikey that if he had
a gyroscopic gunsight early on, it would have made him a more accurate shot. especially in the dogfighting theater
of N.Africa.

I think the purpose of the EZ 42 in Fw190's Me262 where mainly for shooting down heavies. Nice slow moving
a/c. set the span, fire from a relatively safe distance.

 

[davebender]

I doubt experienced WWII era fighter pilots attacked at point blank range because they wanted to. Rather it was the only way to get results. Attacking from 100 meters is inherently dangerous as you are likely to get hit with debris from your victim. Not to mention defensive gunfire from enemy bombers.

Give Erich Hartmann or Stanford Tuck a gunsight that can hit enemy aircraft from 500 meters and that's the range they will shoot from. A significant benefit on top of greater weapons accuracy.

 

[tyrodtom]

Another reason some of the aces preferred shooting point blank was the target took more of the full impact of the round. At 500 meters most rounds are down to about half the velocity of what they were at 100 yards, so energy was down the same. Maybe not so important in explosive 20mm rounds, but very important in .30 and .50 cal because velocity and energy was about all they had to destroy aircraft.

 

[Rivet]

Post #84 by P-40K-5 contains the magic word, "Practice." Several of the posts here are actually beginning to mention names of the "end users" of the equipment in question. You might want to consider the training regime of the people charged with this esoteric trade you consider. Walter Horten was chastised by his squadron commander during his tenure as unit technical officer for opening fire on the British at very long range. Horten got hits, he had an intuitive skill. I think Galland was just jealous.
Mention made of Radar gunsights. A word of caution in trusting them. A Mig 19 was chasing me and locked on a Perigrine Falcon, I got away. Mark your target. Regards

 

[renrich]

Speaking of gun sights, I found something interesting on page 164 of the "Report of the Joint Fighter Conference" on the subject of gunsights and gunnery. Some of you must be familiar with the debate about gunnery training in the different air forces which we have had off and on for the last several months on several threads on the forum. This debate was sparked by a statement made by John Lundstrom in "The First Team." His statement went something like this; "With the partial exception of the IJN, the USN was the only air force in the world which trained their pilots extensively in full deflection shooting." The point he was making was that the USN gunnery training was so extensive that it contributed heavily to the success of the USN trained fighter pilots in WW2.

The statement I am referring to in the book is by Commander Monroe during a discussion about air to air and air to ground weapons and the statement is made when he is talking about the new Mark 23 lead computing sight superseding the old Mark 8 sight. The statement goes like this: "Everybody else in the world has tried it out, the Army and the British were delighted with it but the Navy is not yet convinced it is good. Out training people think very highly of their training method and claim they have the best deflection shots in the world coming out of their schools, so possibly, they argue, the lead computing sight won't help the Navy gunner as much."

To me, that statement adds weight to Lundstrom's statement in his book, although I know it won't cut much if any ice with some on this forum. I do think it is incontestable that the USN was putting a lot of emphasis on good gunnery and especially full deflection shooting. I recently spoke with a friend of mine, a former Marine pilot who flew F9Fs and later A4s in Nam and he told me of the Navy subjecting him to those same old full deflection gunnery runs against a banner or sleeve during his training just as Lundstrom described in his book. Incidently I saw Tex Hill being interviewed during a segment on TV on the AVG and he stated that his training by the USN prior to WW2 was "The best in the world."

 

[Glider]

My hand goes up in the not much ice cut section, but you know that already.

 

[renrich]

Thanks Glider, I somehow knew I could count on you To chime in on the old debate about the efficacy of the 50 BMG I found the following in the "Fighter Conference Report"; During the weapons discussion, there was a lot of testimony about the lethality of the various guns with the 60 caliber seemingly being the weapon of the future. Lots of food for thought but too much to put it all in here. However, the USN seemed to be sold on the 20 MM cannon and asked a AAF rep why the Army was not going in that direction. The Colonel replied, " I will try to answer it in this way. I believe the Army would like to have a lethal density pattern. The most bullets going across one place at a given instance. We would like to have the smallest caliber gun to do the job. As long as a 50 will do the job we feel that if we can carry a greater number of guns and a greater amount of ammunition for the same weight with an equal or greater fire power, that is the gun we want. We can put out more bullets and we can have more weight covering the same area." He goes on to say that with the expert gunner, it makes little difference what gun is used but with the middle or lower gunner(like most pilots in all air forces except the USN ) he needs as much pattern density as he can get in order to get hits. He points out that "with a P47 they sight the guns so that the first two converge at 250 yards, the second at 350 yards, at 450 and at 550. That gives you a density pattern in depth as well as width of around 200 yards. "

All kidding aside, that is a pretty persuasive argument. Kind of like when I am hunting dove or quail, I use 7.5 or 8 shot knowing full well that 6s are more lethal with a single hit. But those birds are so small, at forty yards, if the pattern is not dense, I could have a bird in the middle of the pattern and not get a hit with heavier shot. I get amused with some of the remarks here like aiming at an airplane where we know it is not armored. Good grief, looking at combat films, one can see that in most cases the attacker is just throwing out a bunch of bullets hoping to hit anywhere on the target. 100 yards away is considered close range in ACM. Just imagine though when you are in a cockpit traveling at 300 or so mph and your foe is a football field or a wedge shot away also going 300 mph or so, how small that target looks. Especially end on. Or even more realistic, you are on the tee box of a short par four and you are looking at a green 300 yards away. Imagine a fighter with a wingspan of 30 feet on that green going at 300 mph and think how small he would look.

 

[Glider]

Couldn't let you down

Re the sighting of the guns on the P47 IIRC they also went on to say that no one listened to them anyway, so they started giving out the information and let the units decide for themselves or words to that effect. One reason being that the impact of the fire from two 0.5 wasn't considered sufficient in some cases.
I admit to going out on a limb with this as my copy is packed away and its pure memory, so be gentle if I am wrong.

 

[davebender]

If so then USN aviation must have lived in their own little world. Some of the other USN departments (i.e. torpedo development) were arguably the worst in the world during 1941.

 

[Shortround6]

As long as we are going completely off topic and out of context, perhaps it was the "torpedo development dept" that lived in their own little world.

The steam engineering dept was certainly above average, if not the best.

The Heavy guns were certainly good as were the medium guns, not many designs but then if what you have works why spend a lot of time trying to change.

Provisions for damage control were as good or better than most other navy's.

I could go on but this is off topic.

 

[Kryten]

there is a crossover point where saturation compared to specific damage can lead to much debate, carrying more lighter guns with more ammo requires more hits to do lethal damage, when your deflection shooting it's unlikely you will be able to lead an aircraft long enough to hit with sufficient rounds to bring it down, whereas a single hit with a larger caliber weapon could end the fight there and then?

 

[Shortround6]

As with many things, the best solution is probably in the middle. While a single hit with a large caliber cannon (like a 37mm) will certainly end the fight in very short order, the low rates of fire and high weight of the guns/ammunition (meaning 1 gun per plane usually) results in a very low likelihood of a hit in a defection situation. The usual low velocity of such guns means that they need more "lead" than higher velocity guns which just compounds the problem. Twelve .303s was probably the ultimate in saturation but the projectiles lacked range (lost velocity and energy quickly) and striking power.
The 20mms probably offered the best compromise between rate of fire of a usable battery and effectiveness of hits. The 20mm Hispano, MG 151/20, and 20mm ShVAK were probably the best guns to service in large numbers. AS guns and ammo evolved through the war so did engines/aircraft which allowed later war aircraft to carry heavier batteries of guns.

 

[renrich]

Glider, you are close and your memory is pretty good. What actually was said was that the Navy put out the information about sighting in the guns the AAF way but the Navy said that the way the guns in some of their fighters were installed, the guns jumped around so much that no real convergence point could be obtained and sighting in the guns to provide a pattern exacerbated the problem. Consequently, the advice from BUAER was ignored and the squadrons went their own ways. In my book, "80 Knots to Mach Two" by Linnekin, which I urge all of you to get, he mentions that the 50 BMGs in the wings were mounted loosely and they jumped around a lot when fired.

The point about density of the pattern was that, for instance, because of issues like, down range velocity, rate of fire, number of guns firing, trajectory, at a certain spot on the target, two or three 50 BMGs might impact, whereas only one 20MM might impact. The AAF's position was that with average or poor gunners, the chances of achieving a lethal hit were greater with the six or eight 50s. In simple terms the pattern was more dense. The AAF especially did not like mixed wing gun armaments for the above reasons.

What is interesting about these discussions is that there were many different opinions expressed and there were many issues with any new innovation which impacted the decision whether the innovation was adopted. For instance, the Navy said that all of their current fighters had been designed with telescope gunsights. The adoption of the next generation gunsight was resisted because it was unhandy to use, obscured visibility, and caused head injuries in a ditching. Any innovation which added weight was looked at with a jaundiced eye.

Incidently, during war games in the late 1970, early 80s, F15s mounted Weaver rifle scopes bought at the local sporting goods store by the pilots in the cockpits so that an AC could be more easily seen and identified as enemy or not at a distance.

I don't know what Tex Hill's opinion about pilot training in the USN has to do with poor performance of Navy torpedos early in the war. The performance of German torpedoes in their subs was poor early in the war but that did not alter the fact that the German submariners were very courageous and skilled.

 

[merlin]

In the early '30s the RAF were very impressed with the Hispano cannon, and realised it was the way to go with fighter armament. Previously they had decided to stick to the 0.303" calibre - thinking that the 0.5" didn't give that much advantage.

In OTL they went with the Whirlwind, but because the were delays with production, especially with availability of the engine, alternatives were looked at. Hence late '38 consideration was given to putting cannon in the Spitfire - which resulted in the IB Mk flying in Feb '39. Therefore from the first flight to combat in 19 Squadron in Aug '40 we have at most eighteen months to produce test, and iron out any problems - which didn't prove long enough.
Supermarine Hawker both submitted designs, for the Cannon spec F.37/35, as did other companies e.g. Bristol and Boulton-Paul. at the Design conference in May '36 it was decided to order five prototypes - two Westland, the Supermarine 313 (a twin), and two Boulton-Paul - P.88a (Hercules) P.88b (Vulture). But the Treasury wouldn't support that, and only the Westland prototypes went ahead - the rest is history.
But suppose for a moment the Boulton-Paul aircraft did get built - prototype perhaps late '37 or early '38. So lets assume that the P.88a gets a contract (yes I know there were also problems with the early Hercules) - - seems plausible to me that with the extra time the cannon in the wings problem could have been solved by early 1940!??

 

[Shortround6]

there were two problems with the cannon in the wings, One was that laying the gun over 90 degrees so the the drum was on the "side" rather than on "top" affected reliability. The other is that the gun, having been designed to function while bolted to 1000lb plus of engine, didn't take kindly to being mounted in a flexible (comparatively speaking) wing, the gun needed a forward support partway out the barrel and this support had to connected to the rear mount in a fairly rigid manner. The upright, fuselage mounted guns in Beaufighters and Whirlwinds seemed to have less trouble. With more planes fitted with wing guns for trials progress could have gone faster but the earlier adoption of a belt feed may have also helped.

 

[merlin]

Thanks, Shortround6, that's what I thought. I believe too they were production problems with the weapon in the UK. But with an aircraft that was purpose built for four 20mm cannon, rather than having to adapt an existing design i.e. a 'B' Spitfire wing, seems logical to have more chance of success. On the minus side the Boulton-Paul Dante (I've used this name before for it, so unless anyone else has a better one ... Dante of course as in 'inferno' - after all the cannon fire), won't have the performance of the Spitfire - but I think it would make an impression (!) on the bombers!

 

[Edgar Brooks]

There were few problems with the cannon, themselves; the whole problem was caused by trying to dispose of the empties, after firing. All sorts of curved "deflector plates" were tried, but, due to the wing flexing, none worked. The author of "From Duxford to Karachi" was an armourer on 19 Squadron, and relates the problems they had. Eventually, they gave up on the idea, and, on the Vb (and IIb) the empty case was ejected sideways into a triangular compartment near the wheel well. Once a new feed was perfected, meaning that the guns could, once again, be mounted upright, the problem went away.
The Air Ministry rejected the idea of using 2 x .5" with 2 x 20mm, at first, because they discovered that, from directly behind, a .5" bullet was no better at penetrating German armour than a .303", and from the side, with the average pilot's lack of ability to master deflection shooting, hosing the fuselage with four guns was more likely to disable the pilot. When the gyro gunsight appeared, in early 1944, everything changed, since anyone could master deflection shooting, so the "E" wing was born.
I've been told by a man, who met a man (yes, I know) who'd seen a Spitfire Vc crash; it was one, on test, which had been fitted with 4 cannon, and, when the pilot test-fired them, the wings tore away. Though it sounds somewhat dramatic, it might explain why early "C" wings could not be fitted with 4 cannon, and the 4-cannon wing only became standard in the Spitfire 21.
Edgar