The XA-38 Grizzly

[muskeg13]

GregP: Artillery weapons EFFECTS tables, now built into fire control computers, tell you how many rounds it will take to kill a target once you hit it. My comments are not in reference to small caliber autocannon, like the A-10's 30mm GAU-8, but to 75mm and larger artillery, developd for ground use, but adapted to be carried by aircraft and fired one shot at the time. When you use the same ammo, effects on target will be the same whether the weapon is fired from the ground or the air.

 

[GregP]

Hi muskeg,

Artillery effects tables are NOT built into targeting computers (TCs). They don't tell you how many shots to fire or what the effects will be. TCs only have one function and that is to put the fire on target. If they have ANY tables built in, it would be ballistics and atmospheric tables. They then take those data and use the airspeed, angle of attack data, and current g-force to put the shells on target.

And the 1951 book I have on artillery ballistic mathematics says almost nothing about effects (actually I can't find anything at all about effects). It is entirely dedicated to aiming so the shell hits the target. So it does address circular error of probability (CEP). Artillery effects are a different subject from hitting the target. They are important to military planners, to be sure, but have little to do with placing the shells on target.

I happen to like the WWII 75 mm cannon and I know its punch was much bigger and better than smaller bore cannons. You don't seem to like it and that is surely just fine. This far after the war it hardly matters since I know of no 75's still in use by the USA or by anyone else for that matter.

This started out as a thread about the Beech A-38 and I like the plane, If you don't that's OK. They only made two, so how much difference will it make if our opinions are the same or differ? If it had been designed just a bit smaller and could have used the R-2800 they might have built some for service use. To me it was a good-looking ship that could have been a good one.

In the event we all know it wasn't proceeded with.

 

[muskeg13]

I apologize for taking this thread off topic. Fire control is not the same as targeting. Fire control is also about matching weapon and ammo type to the target type and determining what volume of fire is needed to achieve a certain result, usually to supress, neutralize or destroy a target. Your old artillery book, probably a Table of Fire, wouldn't address this as the weapons effects tables were classified. Your book is about how to hit a target, not about what to hit it with or with how many rounds to use. Weapons effects estimations are incorporated into current artillery fire control computers.

In a B-25H, the navigator/gunner and the pilot have to become their own military planners to determine not only how to achieve "steel on target" but how many shells it's going to take to get the job done.

If the Air Force is going to use Army stuff, maybe they should ask how our stuff is supposed to work, eh?

The reasons I even brought up weapons effects tables were twofold:
1. Both the 75mm and 105mm cannon used in aircraft were originally U.S. Army Field Artillery systems, and when the AAF and USAF decided to use them with U.S. Army developed ammunition, the expected effects on target are already known, documented by artillery firing test (weapons effects) data.

2. Wild claims on this thread that a few (extremely lucky) 75mm hits at or below the waterline on a ship would result in a 'kill" and that the 75mm cannon on 5th AF B-25Gs and Hs are responsible for the demise of the Japanese merchant and naval fleets is pure fantasy, refuted in part, by established artillery weapons effects tables. Given the number of 75mm equipped planes, the ammo they used, the number of shots per target run, it's a mathematical impossibility...it just couldn't have happened.

As tomo pauk and others have stated, the 5th AF became the experts in anti-shipping using skip/glide bombing, and at the same time laid to rest the notion of using HEAVY CALIBER aerial cannon for ground attack. They proved by mid-1944 there were better ways of attacking ground targets.

By the way, I think the XA-38 is a pretty cool design, and it's a very good thing the Luftwaffe hadn't something similar to kill our bombers. A 75mm shell hitting center of mass on a Fortress, Liberator or Lancaster or even a Superfortress would have been catastrophic.

 

[GregP]

Thanks for the good answer and don't worry too much about a small off-topic excursion ... as long as we get back to before too long, but I disagree a bit again. Not with what you stated ... it is ALL true with the exception of the part where the pilots planned the number of hits and the effects ... at least that is what I think.

In reality, they flew the mission and if they saw a ship or other target of opportunity, they might strafe it with the 75 ... maybe. If anti-aircraft fire was absent (merchant ship), they might make multiple passes. If it was a warship and they were stupid enough to strafe it the first time, they would NOT be stupid enough to strafe it twice or more times unless THAT SHIP was the primary target. I cannot think of an instance where strafing a warship was the primary mission for a big-bore cannon aircraft. I might have missed a few, though. We mostly attacked warships with bombs and torpedoes, not with airborne big-bore cannons unless it was a "target of opportunity."

Now if the A-38 had been put into service maybe that might have changed a bit, but I don't think a 75 against an armored warship would be a big threat while the ship would be an enormous threat to the attacking A-38. This was a BIG airplane and, as far as I know, it carried only 20 rounds for the big cannon. But you have to admit, it was a LOT faster and more mobile than the horse-drawn or truck-towed variety of 75.

Since they only made two A-38's, we don't know where they might have been deployed. I rather think it would have been a tank / train buster in the ETO and perhaps maybe a support plane for island invasions in the Pacific. I'm thinking pillboxes and maybe Japanese light tanks. Might have a mission against ships in the MTO or North Africa ... but would probably be mostly against whatever ground targets were moving around or were obstacles. In the desert you can just walk around the obstacle and leave it behind in the sand, so maybe ships were a more likely target in the MTO.

I fully realize the necessity of artillery effect tables for ground warfare, but cannon-armed aircraft didn't usually have anything to do with that concept during WWII. The bombers? Yes. It came into play a LOT for sizing the attack. As long as you HAVE the aircraft, why send more than necessary to hit a target? If you needed more than you had, it resulted in a maximum effort mission. A post-attack BDA would prove the table or not if done in good weather. But throw in smoke, fog, clouds, or any serious weather and the BDA could easily be changed by 60+% just due to weather effects on bomb aiming and by obscuration of the target by clouds.

Not so with Army artillery. Regardless of the weather, stationary targets didn't move around and effects could be predicted with decent reliability. If you can get the Army guys your coordinates, they can place fire VERY close with very good accuracy. Not necessarily so with aircraft. A LOT has to do with the winds aloft, the g-force and angle of attack, and the inherent accuracy of the bombsight, plus any number of other minor factors ... none of which would be present for ground-based artillery attacks.

I LOVE airplanes, but if I needed close fire, I would rather call in an Army artillery attack than depend on a fast-moving plane. Of course, in places like Viet Nam, you might not be in range of artillery and so HAD to depend on the planes. Mostly they delivered well. Sometimes not. Again, weather and the surrounding terrain were big factors along with the karst. We had Skyraiders shooting within 20 meters of us sometimes, but that was only when WE called it in, and their cannons were of the 20 mm variety. What the hell, if you are about to die, then calling in some airborne cannon fire VERY close isn't a bad option.

So I agree with you whole heartedly for ground-based artillery, but am not so sure for airborne big cannons. I think they tried for a hit or hits and hoped for the best given the cannons they were issued with the plane. I have only spoken with two guys affiliated with the big-cannon B-25's and both said the big-guns were devastating to the targets but were never the primary weapon until the bombs ran out ... the big gun-equipped B-25's could still carry a bomb load.

Now the German Henschell HS 129B-3 sometimes had a 75 mm cannon with 12 rounds in the magazine. It was the 7.5 cm Pak 40 anti-tank gun, a lighter-weight, fully automatic aircraft-mountable version, with a completely different and more aerodynamic muzzle brake to produce the Bordkanone BK 7,5 model. It was primarily used as a tank buster on the Russian front. It is supposed to have been a pretty decent attack plane against tanks. I suppose that some 4 to 12 of them flying around a battlefield would have caused a lot of consternation to Soviet tank crews. It sure would have made ME nervous.

Even today, I bet an old Sukhoi Su-25 Frogfoot or two would cause a big pucker factor to a tank crew.

 

[gjs238]

As pointed out earlier, there was a lot of small intra-island boat transport in the PTO.
I imagine cannon and rocket fire were effective against those.

 

[yulzari]

Which was best as an aerial gun - the 57mm 6 pounder with molins autoloader or the US 75mm cannon?

Wuzac. These are not directly comparable as they chosen for different purposes though the Molins autoloading was a definite advantage overall.

The Tetse used the 6 pounder ammunition as it was originally intended as an anti tank aeroplane and the 57mm 6 pounder was a better armour penetrator than the 75mm which used an HE warhead. This transferred quite well to naval use when the RAF realised a Mosquito was too large to survive at low level. The AP round would pass through a depth of water and penetrate a submarine pressure hull if it caught a submarine in the process of diving. The B25 was for use against surface targets so the HE 75mm was the correct choice. As I mentioned above, the Tetse could have gone to a 75mm barrel for HE fire as they did on tanks. The RAF in Burma also used their 40mm S guns on surface targets so preferred using HE rounds to the AP carried in Africa and NW Europe.

The Tetse Molins/ROF gun in a Mosquito was a better package. What the USA had in the Pacific was the B25 and manually loaded guns so that is what they used.

 

[GregP]

Exactly yulzari, we used what we had. If they had another gun, they would have used it, too.

That is almost the entire point I was trying to make earlier. You don't check the table for fire effects and calculate anything ... you use the gun installed in your plane and do whatever is necessary to get hits with it. If you hit the target and nothing bad happens to it, then that target is not one you would continue to select for the aircraft, but you don't have the option of choosing your guns. They arrive with the aircraft and that is what you plan around.

 

[Shortround6]

That is what the guys in the Field do.

The Guys in charge of ordering aircraft from the factory and ordering the guns from their factory had darn well be figuring out fire effects and calculating. That is what they were being paid for.

A lot of the 75mm guns were stripped out and replaced by a pair of .50 cal guns.

 

[bbra]

I have a drawing from the 'net of an OV 10 equipped with a recoilless gun and a 7-round magazine in the cargo area. Calibre is 105mm. I don't know if this was a serious proposal or somebody's doodle. Is it just a coincidence or is it meaningful that the last seriously considered cannon equipped a/c came from the same company? And both are single pilot, twin engined, twin tailed aircraft.
Knowing next to nothing about artillery (like pornography, I know it when I see it, but that's about all), I would assume a modern 105 is more potent than a WWII 75. I don't know what the OV 10 would shoot at in VietNam, but that big gun may have made some FACs happier than the usual 4 .50s the Broncos carried.

 

[GregP]

You are correct Shortround.

Where did you get the info that many 75's were removed and replaced by 50's? Just curious. I'd believe it after about early 1945 or so. Not much left to shoot at with big-bore cannons in the Pacific that was worth the loss of payload.

 

[tyrodtom]

From the link Aozora posted on the 75mm cannon in the B-25, it sounds like they used the cannon for long range AA suppression.

When attacking targets at sea you're usually going to have a long exposed run in to the target. There's nothing to hide your approach, and even their light AA has got a greater range than your .50 cal.

It sounds like they fired the 75's at the beginning of the run, then switched to .50's when they were in range, then dropped a bomb when they got close.

On bigger targets the 75 wasn't used to destroy the ship, it was used for long range flak suppression.