I have seen pictures of early P-38 Lightnings which appear to indicate that a 150 round ammuniton drum was utilized as the ammuniton feed method for the 20mm cannon.  Later models of the P-38 (post P-38F models) appear to have used a belt feed mechanism (smaller drum on the top of the cannon) similar to the BFMs used on RAF Spitfires, Typhoons, etc (aircraft using the 20mm cannon).   The capacity of the 20mm ammuniton for the P-38 has been stated as being 150 rounds.  I am not sure if that figures applies to the stand alone drum or the bfm method.
 
Early RAF Spitfires use a 60 round ammunition drum before changing to the bfm method.  I thought 60 rounds was about as large as the 20mm drums came.  Can anyone confirm if the 150 round ammuniton drum was used for early model P-38s ( up to the P-38F model) and what brought about the change to the belt feed mechanism method? 
 
Thanks.
 
Ron

Ron – Do you have photos of a 150 round drum? I have seen P-38 cutaway drawings showing drums but they appear to be the smaller 60 round variety. There are a number of factors against large drums, but that is not to say they did not exist.
 
B-29’s used a 120 round drum for the Hispano-Suiza in the tail gun mount. Standardization efforts would likely prevent procurement of separate 120 and 150 round examples. Since drums mounted directly to the gun breech, the weight of the drum plus 150 rounds of 20mm ammunition would likely strain the gun’s adjustment points during the heavy maneuvering typical of a pursuit airplane in the P-38 class. Tray assemblies (attached) distributed the weight on the airplane’s armament bay itself, lessening this possibility.
 
Realizing that anything is possible, if you have photos, please post them or PM me if you wish. -Adrian

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Omega7,
 
Thanks for your e-mail.  No, I don't have any pictures of a 150 round drum.  As a matter of fact, I don't think they existed for the Hispano cannon.  The pictures I have seen show a 60 round drum which is mistakenly referred to as a 150 round drum.  The 150 round ammunition supply was the capacity of the belt feed arrangement that you attached in your e-mail (thanks for that).
 
Pictures of the 60 round drum on the P-38 Glacier Girl can be found at the following web site:  http://www.kspg.org/MiddlesboroKSPG03/p38.htm
 
If anyone has any pictures of either ammuniton configuration that they could post, I would certainly appreciate it.
 
Thanks.
 
Ron

Glacier Girl it is intersting to note that they list the aircraft as a P-38E when in fact it is a P-38F-1-LO
 
Terry T.
 

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I have continued my research on the P-38 ammunition feed arrangement and have found no evidence to indicate that the P-38 used the 60 round ammunition drum with the Hispano cannon.  This makes the use of the 60 round drum on Glacier Girl all that much more interesting (questionable?).
 
Is it possible that the drum has been installed in error (not accurate for the aircraft) and it should be replaced with the 150 round magazine and belt feed mechanism?
 
Can anyone shed any more light on this subject?
 
Thanks.
 
Ron

 

Ron - Unless the attached is artistic license, drums were there someplace. The attached is uncredited but appears to be a Lockheed cutaway. Sixty round drums would only provide approx. six or sevens seconds of fire; not a surprise that larger capacity feed mechanisms evolved.
 
20mm’s, when teamed with .50 cals, were more hype than substance. The 20mm was ballistically a DOG that did not approach the .50’s trajectory making harmonization with of a single gun sight difficult. Additionally, the manufacturing tolerances of the Hispano-Suzia required the use of lubricated cartridge cases, resulting in stoppages at high altitude temperatures or a spool-up period before the gun achieved its normal rate of fire. - Adrian

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Adrian,
 
Thanks for the great diagram.  Do you have the full drawing of the P-38 that you could post? 
 
Yes, that is definitely a 60 round ammunition drum.  They must have been used briefly before the 150 round magazine and belt feed system was installed. 
 
I have attached links to some interesting articles covering the use (or lack of) of the Hispano 20mm cannon by the US in WWII.  The articles give some very interesting insight into what some of the problems and thinking were regarding the use of the .50 caliber machine gun and 20mm cannon.
 
Thanks again.
 
Ron
 
http://www.quarry.nildram.co.uk/US404.htm
 
http://www.quarry.nildram.co.uk/CannonMGs.htm
 
 

Ron – Thank you for the links. I have the volume of the Chinn book that covered the Birkigt design. There are errors, but it remains a good reference.
 
Nearly always overlooked in standard works dealing with this subject is the U.S. sale of the cal .50 Browning M2 aircraft gun design to Imperial Japan in 1934. The Japanese eventually scaled up this design to 20mm in size (the Model HO5 that proved outstanding). Six years later, the U.S. bought the manufacturing rights to the Hispano-Suzia design in pursuance of a 20mm gun that never reliably lived up to its task. -Adrian

150 round 20mm ammo can as used in the P-38.  Note that there are about 25 rounds still outside, being fed in.

I have an SB2C Helldiver, 20mm, 120-round  wing ammo can. Basically a tall rectangular box about 18in x 12in x 12in  with an opening on one side at top with plastic rollers for the rounds to slide over and the top opens to one side fully for loading.



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SHAEF1944 American Veterans Museum

Since drums mounted directly to the gun breech, the weight of the drum plus 150 rounds of 20mm ammunition would likely strain the gun’s adjustment points during the heavy maneuvering typical of a pursuit airplane in the P-38 class.

ORIGINAL: omega7

Adrian, the ammo can didnt mount to the gun breech with the 150rd setup.  See pic below.  It mounted on a shelf extending from the firewall, and the feed part of the can overhung the cannon.  You can also see this somewhat in the diagram you posted earlier, but this pic shows the mount a bit more clearly.
 
Also, in the cutaway diagram, the " drum " on top of the 20mm is the electric feed mechanism, which moved the ammo out of the ammo can at left in diagram, along the ammo chute, and into the guns breech.





 

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SHAEF1944 American Veterans Museum

SHAEF 1944,
 
Thanks for posting the pictures.  Much appreciated.  Almost all pictures I have seen of the P-38 show the 150 magazine.  Do you know if the 60 round drum was used very much, if at all?  Sixty rounds sure wasn't much. 
 
The restored P-38 Glacier Girl is fitted with a 60 round drum, but I wonder if that is correct.  All accounts indicate that it is an accurate restoration of the recovered aircraft.  Would you have any information on whether the 60 or 150 round magazine would be correct for that airplane?
 
Thanks.
 
Ron
 
 

SHAEF 1944,
 
One more question.  Which restored P-38 is the color picture that you posted from?  It looks really nice.
 
Ron

Ron,  only other cannon I remember in the P-38 was the very early 37mm installation, and I dont know if those few entered operational/combat service.  If I remember, they only had about a 15 round magazine.  I'll search around for pics of that, but I dont recall having any handy.  Also dont know about the 60rd can for the Lightning, only ever seen the 150rd can, but I'll look around for something like that also.  Maybe something just used for training, ferrying ?

SHAEF1944 American Veterans Museum

SHAEF 1944,
 
Thanks for the information.  The thought that it might have been installed only for ferrying also crossed my mind.  That could be the explanation.
 
The 150 round magazine in the color picture you posted looks interesting.  Do you have any of the belt feed mechanism?  I didn't think it was operated electrically, but rather by an internal spring system.
 
Thanks.
 
Ron

One more armament question.  I notice that later model P-38s seemed to have their .50 caliber gun barrels covered with silver blast tubes - similar to those used on the P-47.  Any idea why they started using the blast tubes on the P-38?
 
Thanks.
 
Ron

Hello SHAEF-

quote:

Since drums mounted directly to the gun breech, the weight of the drum plus 150 rounds of 20mm ammunition would likely strain the gun’s adjustment points during the heavy maneuvering typical of a pursuit airplane in the P-38 class. ORIGINAL: omega7

Adrian, the ammo can didnt mount to the gun breech with the 150rd setup. See pic below. It mounted on a shelf extending from the firewall, and the feed part of the can overhung the cannon.

Not certain of your objective here, but completing the paragraph with the next sentence as I posted it :

...a pursuit airplane in the P-38 class. Tray assemblies (attached) distributed the weight on the airplane’s armament bay itself, lessening this possibility.

puts us in agreement of sorts.

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Also, in the cutaway diagram, the " drum " on top of the 20mm is the electric feed mechanism,

Assuming that you are referring to the cutaway in post no. 6 - the "drum" is: 20-mm 60 round magazine M1, not an "electric feed mechanism". Cartridges were inserted singularly (without links) against the drum’s spring tension. Again, drums did mount directly to the gun’s breech; Tray Assembly did not. See APPLES thumbnail attached.
 
----------------------------------------------
 

which moved the ammo out of the ammo can at left in diagram, along the ammo chute, and into the guns breech.

As illustrated in post no. 2, 20-mmFeed Mechanism AN-M1 was used with the 150 round tray/chute assembly. The Feed Mechanism also had the important function of de-linking ammunition and dropping the links into a chute designed for the purpose, and finally to feed the gun one round at a time, preventing jams in the process. Your shot of "BABE" shows Tray Assembly being loaded for insertion into the armament bay for connection to Chute Assembly 235817 , ultimately connecting to Feed Mechanism. Feed Mechanism came in both left and right hand feeds. The only photo that I have of Feed Mechanism is opposite hand, but will show the mounting position on the gun in either case. See ORANGES thumbnail attached.

Neither of these feed systems used any electric power. -Adrian


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Deleted duplicate post.

Adrian,
 
Thanks for posting the outstanding information!  I really appreciate your efforts in providing answers/clarification to my questions.
 
It woud certainly appear to me that the use of the 60 round ammunition drum on the P-38 was very limited, and probably not used operationally.
 
Ron

Adrian, I was looking at the parts schematic breakdown in Post #2.  Didnt even look that close at the illustration in Post 6.  I was confused because you said you had seen " cutaway drawings showing drums but they appear to be the smaller 60 round variety "  in that post.  My mistake assuming you were posting the schematic showing this in Post 2.  Ooooops, my bad !
 
What was the power source of the AN-M1 Feed, spring, or did the gun power it ?
That small capacity drum in a P-38 is a new one on me, seen tons of pictures of them on 20mm's, but they were all aboardship, shooting at Kamikazes.
 

SHAEF1944 American Veterans Museum

What was the power source of the AN-M1 Feed, spring, or did the gun power it ?

SHAEF – Some of each.

During loading, Feed Mechanism’s driving spring (Section A-A, attached thumbnail) was compressed by winding with a wrench (also attached). Performed manually, this was 20-mm Feed Mechanism AN-M1's initial winding. After the first round was fired, the gun’s recoiling parts re-wound the driving spring for the feedings of subsequent firings through a cam/ratchet arrangement. -Adrian

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