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Martin A-20 20mm top turret drawings and information needed

ACResearcher

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I'm especially in need of a GA 3-view, SIDE VIEW in particular.

Thanks in advance.

AlanG
 

Apophenia

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Alan, Are you after some kind of USAAF Type A-20 turret? (If so, do tell more!) Or, are you looking for details on the Martin turret installed in the Douglas A-20G-20 (and subsequent Havocs)?

If the latter, those A-20s had Martin model 250CE8 and 250CE8A turrets - which the Army designated Type A-11 turrets. AFAIK, all 250CE turrets from 250CE7 to 250CE11 ((USAAF A-3A, A-3C, and A-11 for B-26B/'C, B-24s, YB-40, and A-20s) were essentially similar. Alas, no GA drawings :(
 

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ACResearcher

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Apophenia, I'm looking for the specific Martin A-20 model, 2 - 20mm top turret. It was one of a number of turrets considered for the B-32 Dominator. All I have is the AAF designation which is the A-20 label. There was large amount of research/design done on 4-.50cal. turrets for all locations, 20mm turrets and 37mm turrets done by the U.S. during the war for all sorts of bomber mountings. And toward the end of the war there was fair amount of discussion on turrets that could fit the .60cal mg that Arnold was so enamored of - and which failed miserably. In fact, the AAF switched from the Emerson to the Sperry nose/tail turret because it was felt the Sperry version could be more easily modified to fit the .60 cal. Why the U.S. didn't just copy one of the several 20mm German guns remains a bit of a mystery to me for now, but it may be one of those "not invented here" issues.

Ultimately, post-war the Martin Mercator and early versions of the P2V were fitted with a 20mm ball nose turret (and maybe tail turret, but I just can't picture it in my head right now) and a top 20mm turret as well.

AlanG
 

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Checking my references, most notably the following pair by William Wolf:



I can find no reference to a Martin A-20 top turret with 20mm. There was a Martin A-3-D top turret (two of in fact) with twin 12.7mm MGs as shown below:




The only other variant I have seen is the following from the 2nd XB-32 prototype (supposedly):


What's your source of information - that might help here.
 

ACResearcher

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GTX,

I am not surprised that this turret is not mentioned in any of Wolf's books. There is a HUGE amount of information about the B-32's design, development and operational career that does not appear in his B-32 book, and many turret designs and projects that don't appear in his book on WWII armament. The B-32 will be extensively and deeply covered in Nicholas Veronico's and my book on the subject, currently in preparation. And when we get to our book about turrets you will be shocked by much of what we've uncovered - but that latter book is still in data gathering and organizing mode.

My source(s) of information are original USAAF, Consolidated, aeronautical labs and subcontractor's files and photos, plus a number from other researchers, archives and museums around the country. I will have to discuss posting any of this with Nicholas before I put anything here. I've spent a tremendous amount of time and money researching both these topics and gathering original source photos, drawings and documents (23 GIGABYTES worth at last count) and am somewhat loathe to put too much out on the web before the books go to the publisher. The Martin A-20 turret is a perfect example of this. Prior to my posting the question no one seems to have ever heard of it. I'd like to keep things that way to enhance the historical value and impact of the books. There are a lot of "gatherers" who lift things out of other people's publications and manuals and call it research.

It isn't.

Respectfully submitted,

AlanG
 

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Fair enough - keen to hear more about the books you are working upon and their timeline for publication.
 

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Why the U.S. didn't just copy one of the several 20mm German guns remains a bit of a mystery to me for now, but it may be one of those "not invented here" issues.
The T-24 copy of the MG-42 was pretty much a disaster, which may have soured the US on further German copies. If there's something on it anywhere I'd guess Chinn's The Machine Gun as likeliest to have covered it.
 

iverson

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Why the U.S. didn't just copy one of the several 20mm German guns remains a bit of a mystery to me for now, but it may be one of those "not invented here" issues.
The T-24 copy of the MG-42 was pretty much a disaster, which may have soured the US on further German copies. If there's something on it anywhere I'd guess Chinn's The Machine Gun as likeliest to have covered it.
Someone who knows more about guns can probably give a better account. But Army Ordnance did indeed copy the German MG151-20--sort of.

Unfortunately, they first insisted on converting it to use US, Hispano-type, 20x110-mm ammunition, a 0.60-in caliber cartridge developed in-house for an antitank rifle, or a 12.7x110-mm cartridge that combined the 0.50-cal bullet with the Hispano case. The original German gun was designed for 15x96-mm or 20x82-mm cartridges and muzzle velocities (mv) between 800 and 700 meters/sec. The larger Hispano 20-mm round had a mv between 800 and 900 meters/sec, while the 0.60-cal (15.2-mm) round reached 1,100 meters/sec. I've attached a picture of the 0.60-cal T17E2.

I'm not a firearms engineer. But redesigning a gun to use so much longer and more powerful ammunition in war time does not seem straightforward--or wise. I've read that quite a few of these guns were made, but never used, even though ammunition was available. So I doubt they worked particularly well.

"Not invented here" was undoubtedly a problem in the Ordnance Department. They messed up the Hispano with their own "improvements" as well.
 

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RyanCrierie

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In July 1945, there were studies on re-arming the PB4Y-2 with replacing .50 caliber turrets with 20mm turrets and there was a line:

"Armament has contracted for the delivery of bow, aft deck, and side waist 20mm turrets..."

With all being ready for ground testing by 15 December 1945.

Armament expected drawings of them by 15 August, and would then forward them to CVAC San Diego.
 
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