Browning says demand for M2 is booming

[bojan]

US could stay with .50 for aircraft armament because they could afford to put 6-8 of those in their.

Tough luck trying to do the same with Bf 109, Yak or Spitfire.

 

[Markus Becker]

Good point, I recently saw quite a few warbirds and the 109, 190 and Spitfire are smaller than P-51, not to mention F4U. 

Also, it's not like you absolutely have to have 20s if the biggest target is a twin engine medium bomber. 

[Interlinked]

14 hours ago, bojan said:

1st one was German 13mm Maxim TuF

Browning M1921, .50 Vickers and 13mm Hotchkiss continued this path. Soviets tried, but decided against enlarging Maxim MG, weapon was considered too heavy.

Then M2 appeared as as lightweight version of water cooled M1921.  At about same time DShK (or to be more exact drum fed DK) appeared, but for various reasons did not see production until it was converted to belt feed by Shpagin, giving birth to DShK.

Post WW2 Soviets seriously updated DShK with new feed system, leading to DShKM obr.1946. version, which is what people think about when they say DShK.

I would put water cooled ones, Hotchkiss and DK to a 1st generation, with M2 and DShK being 2nd.

NSV would be 3nd, one that did not happen in the west due the abundance of M2s post war (IIRC no new M2 receiver was made from the end of WW2 until 1990s, that many were made during WW2...). Compared to that, Soviet pre/during WW2 production of original DShK was relatively small, so post war they kept producing upgraded version, and switched to NSV because that was economical thing to do, with savings in production compared to the amount they needed covered cost of retooling easily.

Well, M85 certainly cannot be ignored as the "3rd generation" heavy machine gun of the U.S. Whether the M2HB should be considered "1st" or "2nd" generation is not so clear to me, because mechanically the M2HB was just an M2 re-tuned for a heavy barrel, and mechanically the M2 was just an re-sized M1917. The DShK coming in much later does not really justify labeling it a 2nd generation gun, it just came late. From a technological point of view these guns are basically at the same level and conceptually they are the same.

When we get to the M85 and NSV though, we see a new concept. Firing controls were no longer built into the gun. Instead, the guns were a module in a system, which included a sight module and trigger module separate from the gun. The M85 was meant for a rigid mount and recoil impulse was smoothened by the short recoil action, while the NSV was meant to reciprocate in a shock absorbing mount. We also see a systematic design effort on shortening the receiver by minimizing bolt length by choosing new locking methods and by using new feed systems that took up receiver width rather than receiver length. But energy management in the NSV was leagues ahead. The NSV had more reciprocating momentum because it had a bolt carrier, while the M85 had just the bolt. The NSV bolt carrier had 2 rollers supporting its weight on the receiver guide rails, plus 1 lateral roller on the right to control lateral alignment. The entire bottom face of the bolt carrier was shaped into a long track in which the roller of the feed rocker arm rode (also controlling lateral bolt carrier alignment). The rocker arm rotates a shaft which goes to the top of the receiver, where there is another rocker arm mating to the articulating linkages in the top cover, and those linkages move the feed pawl side to side. Thus the NSV gets high belt pull force over a long pull time, with minimal energy lost to sliding friction in both recoil and counterrecoil. 

Plus, like the DShK, the NSV had de-linkers. The pointy ends of the de-linkers (the shiny pointy bits on the feed tray in the image below) go into the gaps between the belt link and the cartridge, and as the belt got pulled in, the cartridge gets pried off the belt by the curved shape of the de-linkers. The de-linked cartridge is positioned to be fed into the chamber with hardly any energy at all from the returning bolt. So in a first-shot condition (bolt held by sear, return spring at cocked position is the only source of energy), a dirty gun with dirty belts should feed and fire fine even when pointing straight up to shoot at aircraft or something, because the hard parts of feeding were already done by the previous cycle.

The M85 energized its feed mechanism from the short recoil stroke of its barrel extension. The barrel extension pushed on the short end of a feed actuator lever, and the long end of that lever had a slot in it, fitting a lug from the end of a feed lever in the top cover, and the other end of that feed lever moved the feed pawl side to side. The short recoil supplies plenty of belt pull force but over a short time, so the belt is jerked roughly. That is almost certainly the cause of its sensitivity to the belt alignment and feed angle, but I can't speak on any of its other issues. The lack of a de-linker and subsequently higher sensitivity to belt cleanliness and gun elevation angle explains why the M85 was less reliable in the low ROF mode. The low ROF mode was achieved by blocking the bolt assembly from reaching the buffer spring during recoil, so excess recoil energy was lost rather than returned for counterrecoil. Every cycle in the low ROF mode was therefore functionally the same as a first-shot condition.

Economically I strongly doubt NSV made any sense. New 12.7mm machine guns simply weren't needed in big numbers. During WW2 there was an urgent need for more DShKs since single DShKs on a tripod formed the backbone of infantry air defence, and the next lower air defence weapon below 37mm guns. By the 1960s, 12.7mm machine guns were no longer seen as an infantry weapon except in rare cases for airborne infantry and potentially mountain infantry. It was also needed only in small numbers as fortress guns. By far its biggest role was as an AA MG on tanks and occassionally self-propelled artillery. Lighter AFVs had either a 7.62mm, or a 7.62mm + 14.5mm. For export and licensing, NSV production was tied to tank production license in WP, similar to how the M2HB spread in W. Europe because it came packaged with tanks.

[Ol Paint]

https://fnamerica.com/products/military/fn-m3p/

https://fnamerica.com/products/weapon-systems/fn-m3m-gau-21/

Doug

[R011]

3 hours ago, bojan said:

US could stay with .50 for aircraft armament because they could afford to put 6-8 of those in their.

Tough luck trying to do the same with Bf 109, Yak or Spitfire.

 

 They probably could put six five ohs in a Spitfire (or any contemporary British fighter ).  They could fit eight .303s or up to four 20 mm.

[bojan]

No, space in wings was limited, 4 was max possible, which was considered inferior to mixed 20mm + 4 x 7.62mm or 2 x .50.

4 x 20mm was IIRC only with the last wing type, pretty late in war. and it is doubtful you could fit 6 x .50 since wing became too thin outside where guns were mounted. Don't forget that even early Mustangs could not fit 6 x .50 and had to be limited to 4.

Hurricanes and Hurricane/Typhoon/Tempest with it's thicker wing could probably fit 6 x .50, but 4 x 20mm was better armament so Brits did not bother.

[R011]

Six fifties worked well against German fighters and well enough against German medium bombers.  Almost overkill against lightly built Japanese aircraft. The USAAF/USAF kept it too long, though.  They were barely good enough against MiG-15s.  Still, at least the US Navy wanted 20 mm.

[EchoFiveMike]

The USN had institutional knowledge of carrier defense and being forced to stop Kamikazes.  If the AAC or USAF had airfields getting plastered on a routine basis, they'd likely have similar perspective.  S/F....Ken M

[17thfabn]

5 hours ago, R011 said:

Six fifties worked well against German fighters and well enough against German medium bombers.  Almost overkill against lightly built Japanese aircraft. The USAAF/USAF kept it too long, though.  They were barely good enough against MiG-15s.  Still, at least the US Navy wanted 20 mm.

Seems like one of the hold ups in getting 20 mm onto U.S. fighters was the poor quality of U.S. manufactured 20 mm auto cannons during World War II. 

And as has been said before the .50 was adequate against fighters in World War II. I've seen it argued that on a weight of weapon vs. effect 4 20 mm was much more effective than 8 .50 cal. 

[R011]

3 hours ago, EchoFiveMike said:

The USN had institutional knowledge of carrier defense and being forced to stop Kamikazes.  If the AAC or USAF had airfields getting plastered on a routine basis, they'd likely have similar perspective.  S/F....Ken M

The USN wanted 20 mm before they encountered kamikazes.

[17thfabn]

4 minutes ago, R011 said:

The USN wanted 20 mm before they encountered kamikazes.

The USN had a lot of experience with 20 mm as an anti aircraft weapon on ships.

The US Army continued to  use .50 cal as an anti aircraft weapon throughout World War II in single water cooled mounts and double and quad mounts. 

[Markus Becker]

4 hours ago, EchoFiveMike said:

The USN had institutional knowledge of carrier defense and being forced to stop Kamikazes.  If the AAC or USAF had airfields getting plastered on a routine basis, they'd likely have similar perspective.  S/F....Ken M

The US Army didn't take air defense lightly. They didn't have a 20mm AA gun but the far better 37mm. And they had it by 1940 already.  

[Markus Becker]

1 hour ago, 17thfabn said:

The US Army continued to  use .50 cal as an anti aircraft weapon throughout World War II in single water cooled mounts and double and quad mounts. 

And in combination with a 37mm or 40mm gun. 

BTW, didn't the M2 make a comeback with the USN when Kamikazes showed up because they could be installed in places where a 20mm couldn't and to quote Animal House lots of guns were needed. 

[seahawk]

14 hours ago, bojan said:

US could stay with .50 for aircraft armament because they could afford to put 6-8 of those in their.

Tough luck trying to do the same with Bf 109, Yak or Spitfire.

 

No, because the Army Air Force mostly fought enemy fighters. The US navy embraced the 20mm much faster, as they had to actually down aircraft quickly to defend the carriers. 

[Markus Becker]

7 minutes ago, seahawk said:

No, because the Army Air Force mostly fought enemy fighters. The US navy embraced the 20mm much faster, as they had to actually down aircraft quickly to defend the carriers. 

They did but they didn't expect that. Being into heavy bombers they expected that other air forces would be as well. Thus cannon armed fighters like the P-38 and P-39, that didn't work as intended for a long time or at all but that's hindsight. 

The .50 was used because it was available and reliable. 

 

Navy use of the 20mm HS 404 was even more limited than I thought. According to my book just 200 cannon armed Corsairs were made during the war. I'll look up the Hellcat's numbers later but from what I see on Wiki it was very small potatoes too. 

[R011]

2 hours ago, Markus Becker said:

The US Army didn't take air defense lightly. They didn't have a 20mm AA gun but the far better 37mm. And they had it by 1940 already.  

British ground forces, Army and RAF, used 20 mm guns with 40 mm guns just as the RN and USN used both calibers 

OTOH, the US Army practice of putting 50 cals as vehicle mounts on just about every tank and many trucks priced quite useful

[R011]

2 hours ago, Markus Becker said:

And in combination with a 37mm or 40mm gun. 

BTW, didn't the M2 make a comeback with the USN when Kamikazes showed up because they could be installed in places where a 20mm couldn't and to quote Animal House lots of guns were needed. 

Not that I've seen.  You could fit an Oerlkon wherever a fifty would fit  and they did.  They also added  more 40 mm.

  They found even 40 mm too light for kamikazes and developed an improved mount for the 3 inch 50 caliber AA gun to replace them.

[Stuart Galbraith]

17 hours ago, bojan said:

US could stay with .50 for aircraft armament because they could afford to put 6-8 of those in their.

Tough luck trying to do the same with Bf 109, Yak or Spitfire.

 

They did get  2 of them in the later E type wing.

https://en.wikipedia.org/wiki/Supermarine_Spitfire_(late_Merlin-powered_variants)

 

E type

Structurally identical to the C wing. The outer machine gun ports were eliminated; although the outer machine-gun bays were retained, their access doors were devoid of empty cartridge case ports and cartridge deflectors. The new wing allowed for a four cannon armament and the inner bays could carry heavy machine guns. There were thus two possible weapon fits: either

• 2 × .50 cal Browning M2 machine guns with 250 rpg in the inner bays and 2 × 20 mm Hispano Mk II cannon with 120 rpg in the outer bays

or

• 4 × 20 mm Hispano cannon with 120 rpg^[4]

The .303 machine guns mounted in the outer wings were no longer fitted, because rifle calibre bullets were ineffective against heavily armoured aircraft. (These outer guns had always been the less effective part of a Spitfire's armament: their distance from the centreline made them hard to harmonise and in turning engagements, wing flexing meant that the rounds were even more widely scattered). The 20 mm Hispano cannon were moved outboard and the .50 calibre Browning M2/AN, with 250 rpg were added to the inner gun-bays. The first trial installation (modification 1029) was made in BS118 in November 1943; by mid-March 1944 the first service Spitfires to be modified were from 485 (NZ), 222 and 349 Squadrons. Spitfires with this armament were at first referred to as Spifire LF.IX .5 and the E suffix was not officially introduced until early 1945. This armament was standard for all Spitfire Mk IXs and XVIs used by the 2nd Tactical Air Force as fighters and fighter-bombers from shortly after D-Day.^[7] It proved more effective for both air-to-air engagements and air-to-ground attacks.^[9]

 

[Stuart Galbraith]

12 hours ago, bojan said:

No, space in wings was limited, 4 was max possible, which was considered inferior to mixed 20mm + 4 x 7.62mm or 2 x .50.

4 x 20mm was IIRC only with the last wing type, pretty late in war. and it is doubtful you could fit 6 x .50 since wing became too thin outside where guns were mounted. Don't forget that even early Mustangs could not fit 6 x .50 and had to be limited to 4.

Hurricanes and Hurricane/Typhoon/Tempest with it's thicker wing could probably fit 6 x .50, but 4 x 20mm was better armament so Brits did not bother.

E type wing was March 44, so not that late really.

There was an earlier wing on the Spitfire VC around 42/43 that had 4 20mm cannons, but it was deleted because it reduced the rate of turn, the Spitfires best party trick.

 

The 303 remained too long in British service its true, though to be fair there was a large effort to try and replace the tailgun turrets on lancasters with .50, even going so far as to give them a tail mounted radar system to engage nightfighters.

[bojan]

8 hours ago, R011 said:

The USN wanted 20 mm before they encountered kamikazes.

Because they, just like British, Soviets* and Germans have realized that due the increase of the fighter aircraft speed most fighter pilots will, even if lucky get only a single opportunity to engage other fighter during a single mission, so it was imperative to make that opportunity as likely as possible to produce shutdown. If this came with penalty of reduced ammo - it did not really matter, since,  ammo was both more deadly and most pilots would be lucky to get even single good pass on target.

USAAF, planned on multiple engagements during single mission, part of which was due the need for bomber escorts, where fighter armament had to have large amount of ammo. Hence .50s were OK., because even if German fighter was "just" damaged it would be hard pressed to continue attack on bombers. Strictly speaking USAAF bomber escorts did not have to shoot down even single fighter, their mission would be still successful if bombers were protected. Other part of it was overly optimistic, pre-war based mission planning where they wanted single flight of fighters to engage multiple smaller enemy groups. Which did not happen IRL, but that thinking was popular before WW2.

*Soviets are interesting case, they have never faced heavy bombers but have ended war concluding that ideal fighter armament would be 2 x 23mm + 37mm, which they did put in the MiG-15 - again, because if you only get a single pass you better make it count. French and British came to the same conclusion, hence development of DEFA and ADEN cannons post-war, development of which started already in 1946-47s, when there was no threat of the Soviet bombers anywhere in sight.

IOW, USN got it right, USAAF got it wrong. Both for good reasons, but that is how it turned out.

 

[bojan]

3 hours ago, Stuart Galbraith said:

They did get  2 of them in the later E type wing.

2, not 6.

Even with cannons removed there was no place for more than 4, hence Brits decided that 20mm was better choice if you can fit only limited number of guns.

[bojan]

7 hours ago, 17thfabn said:

The USN had a lot of experience with 20 mm as an anti aircraft weapon on ships.

The US Army continued to  use .50 cal as an anti aircraft weapon throughout World War II in single water cooled mounts and double and quad mounts. 

Problem is that role of AD is fundamentally different than that of the fighter armament.

For AD any pilot that flinched and missed due the loads of tracers coming his way was a success. Well, until kamikaze, but even then it might have worked sometimes.

Fighters had to actually shoot down their opponents.

OTOH, engagement ranges for AD vs fighters were quite different, with fighters 500m was especially long and unlikely shot, usually considered pure waste of ammo and warning of potentially unaware opponent that someone was on him. Most aces opened fire at very close distances, usually 100-200m.

For AD distances were larger, even .50 and 20mm were expected to engage to about 1km - original .50 quad mount manual says "effective engagement range is 3/4 mile"(~1.2km), for 20mm it was ~1.5km etc.

 

[Markus Becker]

26 minutes ago, bojan said:

2, not 6.

Even with cannons removed there was no place for more than 4, hence Brits decided that 20mm was better choice if you can fit only limited number of guns.

He meant two per wing and 4x20mm beats 6x.50. 

[Rick]

7 hours ago, bojan said:

Because they, just like British, Soviets* and Germans have realized that due the increase of the fighter aircraft speed most fighter pilots will, even if lucky get only a single opportunity to engage other fighter during a single mission, so it was imperative to make that opportunity as likely as possible to produce shutdown. If this came with penalty of reduced ammo - it did not really matter, since,  ammo was both more deadly and most pilots would be lucky to get even single good pass on target.

USAAF, planned on multiple engagements during single mission, part of which was due the need for bomber escorts, where fighter armament had to have large amount of ammo. Hence .50s were OK., because even if German fighter was "just" damaged it would be hard pressed to continue attack on bombers. Strictly speaking USAAF bomber escorts did not have to shoot down even single fighter, their mission would be still successful if bombers were protected. Other part of it was overly optimistic, pre-war based mission planning where they wanted single flight of fighters to engage multiple smaller enemy groups. Which did not happen IRL, but that thinking was popular before WW2.

*Soviets are interesting case, they have never faced heavy bombers but have ended war concluding that ideal fighter armament would be 2 x 23mm + 37mm, which they did put in the MiG-15 - again, because if you only get a single pass you better make it count. French and British came to the same conclusion, hence development of DEFA and ADEN cannons post-war, development of which started already in 1946-47s, when there was no threat of the Soviet bombers anywhere in sight.

IOW, USN got it right, USAAF got it wrong. Both for good reasons, but that is how it turned out.

 

Regarding the Soviets, did fact that several U.S. 4 engine bombers, including some B29's, cause the choice for the heavy armament for the MIG 15?

[Markus Becker]

21 hours ago, bojan said:

USAAF, planned on multiple engagements during single mission, part of which was due the need for bomber escorts, where fighter armament had to have large amount of ammo. Hence .50s were OK., because even if German fighter was "just" damaged it would be hard pressed to continue attack on bombers. Strictly speaking USAAF bomber escorts did not have to shoot down even single fighter, their mission would be still successful if bombers were protected. Other part of it was overly optimistic, pre-war based mission planning where they wanted single flight of fighters to engage multiple smaller enemy groups. Which did not happen IRL, but that thinking was popular before WW2.

That's what ended up happening but it wasn't planned at all. The so called Bomber Mafia was 110% convinced that bombers didn't need a fighter escort in the first place. Allegedly so much that they even stonewalled the introduction of long range version of the P-47 that could have been operational much sooner than the P-51.

I'm going that they continued to the .50 because that's all they had. They certainly wanted cannons but could not make them work.