1942: What if the American Hispano HS.404/M2 worked?

[ShVAK]

So let's say the M2 is a success, and USN (who were already desiring 20mm cannons across the board) and USAAF decide to put it in widespread service. Would you focus on all-cannon armament or do what the Germans did and use mixed LMG/HMG/20mm setups?

How would you implement 20mm armament on the following craft:

P-38
P-39
P-40
P-47
P-51
F4F/FM-2
F6F
F4U
SBD
TBF
A-20
A-26
B-17
B-24/PB4Y
B-25
B-26
PBY
PB2Y
PBM

I know a few of these already used 20mm historically in some marks (or across the board in the P-38's case) but feel free to get creative with it.

 

[Shortround6]

P-38-change to 3 20mm guns
P-39-one through the hub with belt feed is as good as it gets. extra machine guns to taste.
P-40- forget it.
P-47 put two in wach wing
P-51 one or two in each wing. Planes with one 20mm in the wing get one .50 cal in each wing.
F4F/FM-2 forget it.
F6F go with historic set up.
F4U, go Historic, just more of them.
SBD WHY??? you have about 1200hp, is it a bomber or strafer? make up your mind.
TBF, same deal. sticking in hundreds of extra pounds of guns and ammo cuts into fuel/range or bomb load.

B-17, B-24, B-26, PBY, PB2Y, PBM: The Hispano is much harder to fit in a power turret than the .50. It is too big to manhandle as a flexible gun. A number of these aircraft have no business trying to strafe and aren't maneuverable enough to really bring fixed guns to bear on most other aircraft. and like the single engine attack bombers, multiple 20mm guns are only going to come at the cost of payload or range.

As for the A-20, A-26 and B-25, what is the goal? The 20mm don't really have much more range than the .50s for ground attack. Unless you cut into the bomb load you can replace .50s on a one 20mm for every 1 1/2 to 2 .50 cal fixed guns depending on ammo load. B-25 with 12 Fixed .50s is down to 6 or 8 20mm with less firing time. Against some targets it would be better but against others it maybe worse. Let the fighters strafe with 20mm guns and let the bombers bomb.

 

[davebender]

Probably has less range. However 20mm HE is much more effective vs soft targets.

 

[Glider]

P-38-change to 3 20mm guns
P-39-one through the hub with belt feed is as good as it gets. extra machine guns to taste.
P-40- forget it.
P-47 put two in wach wing
P-51 one or two in each wing. Planes with one 20mm in the wing get one .50 cal in each wing.
F4F/FM-2 forget it.
F6F go with historic set up.
F4U, go Historic, just more of them.
SBD WHY??? you have about 1200hp, is it a bomber or strafer? make up your mind.
TBF, same deal. sticking in hundreds of extra pounds of guns and ammo cuts into fuel/range or bomb load.

The only change I would make to the above is the F6 which I would stick with the 2 x 20mm and 4 x HMG as allowed for in the F6-F5

 

[ShVAK]

P-40- forget it.
F4F/FM-2 forget it.
SBD WHY??? you have about 1200hp, is it a bomber or strafer? make up your mind.

I floated the P-40 as a possibility because it was frequently pressed into the ground attack role on some fronts (like the 20mm-armed and 40mm-armed Hurricane). Why not a 20mm in each wing and two .50s in the cowl? Or ditch the cowl guns and put two 20mm in each wing?

Seeing as the FM-2 served right up to the end, I wonder if it could have a 20mm in each wing. It wouldn't have mattered too much, the Zero was a flyweight under .50 cal fire as were most Japanese aircraft. Might've helped against ships?

I only mentioned the SBD because of the SB2C-4, which had a pair of 20mm in the wings. Obviously a much bigger plane than the SBD so probably not a good basis for comparison.

Unless you cut into the bomb load you can replace .50s on a one 20mm for every 1 1/2 to 2 .50 cal fixed guns depending on ammo load. B-25 with 12 Fixed .50s is down to 6 or 8 20mm with less firing time.

Or you could mount 4 20mm, with more ammo, and a couple of .50s. Or something like that.

 

[riacrato]

yeah pretty much as sr6 and glider put it.
p-51 i'd definetly go mixed just like the spitfire with one hispano and one hmg per wing.
the offensive armament of medium bombers i'd definetly change to incorporate at least 2 if not 4 cannons and the rest hmgs. defensive armament is better equipped with browning i think, bit i'd trial if the taigunner should get the 20mm instead.
later in the war it'd be interesting to see if p-47s could cope with 3 cannons or 2 cannons and one hmg per wing and if that was worth it in the fighter bomber role.

 

[Shortround6]

I floated the P-40 as a possibility because it was frequently pressed into the ground attack role on some fronts (like the 20mm-armed and 40mm-armed Hurricane). Why not a 20mm in each wing and two .50s in the cowl? Or ditch the cowl guns and put two 20mm in each wing?

Seeing as the FM-2 served right up to the end, I wonder if it could have a 20mm in each wing. It wouldn't have mattered too much, the Zero was a flyweight under .50 cal fire as were most Japanese aircraft. Might've helped against ships?
.

The P-40 was a bit overloaded to begin with. You can't keep the cowl guns and move to the -39 and later engines. they used a different reduction gear which moved the prop shaft 6 in higher than the early P-40s. There was a provision to carry a 20mm under each wing on the D/early Es but it was never taken up.

With the FM-2 you would be trading 2 .50s for each 20mm. The 20mm set up should give better results but you are trading 20 shells per second for 48-52 .50 cal bullets per second. It really isn't going to matter against big ships and I don't know how often the FM-2s were used for barge busting.

 

[CobberKane]

Substituting 20mms for .50s would have given a lot more destructive potential for a given firing time, but it would also have cut down on total firing time. So I would be asking , is the exra punch needed needed to the degree that I'm prepared to give up firing time? In the PTO, where most of the opposition is pretty fragile, maybe not. In the ETO, where the fighters are in the air for many hours doing escort work and may be engaged in extended fights, again, maybe not. But in the post D-day ground attack roll, when base is much closer and you just want to put as much hurt on the target in as short a time as possible, then maybe cannons would be nice.
One thing i would definitely have done was get rid of that 37mm on the P-38. Stick 'em all on PT boats, where they're appreciated

 

[Shortround6]

The firing time depends on the plane. the F4Us with 20mm cannon carried over 200 rounds per gun. The F6F-5 carried 225 rounds per 20mm when they carried 20mm guns. The smaller fighters would have been much more restricted in ammo load. P-51Ds carried only 270 round for the 2nd and 3rd gun in each wing so they would be down to only 2 guns when a P-47 with 4 four 20mms ran out. A P-38 with three 20mm might be able to haul over 200rpg.

 

[CobberKane]

The firing time depends on the plane. the F4Us with 20mm cannon carried over 200 rounds per gun. The F6F-5 carried 225 rounds per 20mm when they carried 20mm guns. The smaller fighters would have been much more restricted in ammo load. P-51Ds carried only 270 round for the 2nd and 3rd gun in each wing so they would be down to only 2 guns when a P-47 with 4 four 20mms ran out. A P-38 with three 20mm might be able to haul over 200rpg.

Which doubtless would have been part of the trend towards bigger, heavier fighters towards the end of the war
Of course, with straffing reduced firepower and more firing time could become a drag. Against defended targets I would definitely prefer one run with cannons rather than three with machine guns for the same effect. Get in, get, out, go home

 

[Jabberwocky]

Historically, usage of the Hispano by the US is going to change very little.

When used in concentration of 4-8 guns, the .50 was sufficiently hard hitting to bring down all common opponents that US fighters faced. The only major drawback is the space and weight such an installation takes up.

Swapping the standard 6 x .50 arrangement on most US fighters for a 2 x 20 mm and 2 x .50 cal arrangement isn't really going to save much weight or space. Much depends on how much ammunition you want to carry.

Installed weight of a single M2 Browning was about 74-78 lbs, depending on the installation and ancillaries.

Installed weight of a Mk II Hispano was about 135 lbs.

In terms of raw gun weight, you'd save about 30 lbs, albeit with an increase in firepower of around 30%.

There are a couple of issues to raise though.

Reliability. The M2 browning was generally about 2.5-3 times less likely to have a stoppage than the Hispano Mk II. US Hispano jammed about once every 500 rounds in 1944. In 1944 and 1945, the UK Hispano had one about every 1600 rounds.

In comparison, US Eight AF stoppage rates for the M2 were about 1 per 1450 rounds (dragged down by the P-51B/C, which saw a failure every 900 rounds or so). 2TAF stoppage rates for the M2 Browning were about 1 per 3400 rounds.

Drag. The Hispano is a long gun. Its about 252 cm with the muzzle break, or about 105 com longer than the short barrelled M2 Brownings used in US aircraft.

As a result, a large chunk of the gun is going to stick out of the wings, causing drag. 2 x 20 mm Hispanos cost the Spitfire about 6-8 mph in top speed.

 

[bob44]

For a fighter, I would like to have 6 or 8 50cal. no 20mm, in the wings set for a wide spread. Fast and good firepower for downing a fighter.
For a bomber destroyer, 4 20 or 30mm in the nose, cowl, wings, firing straight ahead. Devastating on a slow, bigger target. A P38 with 4 20mm in the nose?
For a ground pounder, again, 4 20 or 30mm. Although P47s did well with the 50cal.
For bomber defence guns, 50 cal. No sense having slower 20mm guns against a fast fighter.

 

[wuzak]

Swapping the standard 6 x .50 arrangement on most US fighters for a 2 x 20 mm and 2 x .50 cal arrangement isn't really going to save much weight or space. Much depends on how much ammunition you want to carry.

The 0.5" Browning fitted in the same gun bays as the Hispano in the Spitfire.

Installed weight of a single M2 Browning was about 74-78 lbs, depending on the installation and ancillaries.

Installed weight of a Mk II Hispano was about 135 lbs.

A quick search couldn't get me definitive figures, but that seems a little lop-sided to me.

Wiki has the M2 Browning at 38kg and the Hispano at 43kg. That would be an 11lb difference, not the nearly 50lbs you quote. What is included in your numbers?

The Hispano is a long gun. Its about 252 cm with the muzzle break, or about 105 com longer than the short barrelled M2 Brownings used in US aircraft.

What about the Hispano Mk V?

As for reliability, surely that could be fixed with a competent manufacturer?

 

[CobberKane]

Historically, the imperative was generally towards cannon. Fighters got bigger, tougher and more heavily armed. You can only stick so many .50's on a plane, I guess.
If a reliable 20mm had been available to put on the P51 or P47 before it became clear what kind of opposition they would be facing, it would have made good sense. But apparently it wasn't available, and the tried and trusted .50 was used and found to be fine against targets up to the size of medium bombers, which is what those planes wound up facing. So introducing 20mm after that point probabaly wasn't worth the effort and disruption.
If the American fighters had been tasked with intercepting heavy bombers I suspect they would have gone to 20mms very quickly. Any one disagreeing might want to skip over to the 'Martlet compared to European fighters' thread where you will be able to find contributors who believe that a two second burst from 4x.50 could rip a B-17 in half, or the LW fighters may have been over-gunned for heavy bomber interception. Go for it - its a riot!

 

[drgondog]

The choice of installing 20mm in either P-47 or P-51 in 1943 through D-Day would not, IMO, have been a better choice for the primary mission of fighters in the ETO or even PTO. The MTO however placed a much higher emphasis on ground attack than the ETO and PTO and a 20mm might have been a better choice. From my perspective, range and speed of the Mustang was more important to the defeat of the LW over Germany than a much more powerful battery of guns. The P-51 with same engine as P-51A was 6-8 mph slower with the four 20mm due to the incremental drag of those big honking barrels of the Hispano's.

The LW pilots I have discussed this with vis a vis P-51 vs Me 109 or Fw 190 commented that perhaps many more German fighters would have fallen had the 51 been armed with a reliable 20mm and conceeded that the trade off would be the degradation in airspeed and resultant range associated with a 3=% increase in drag for the 4x20mm configuration on a P-51B.

There are so many Encounter reoprts describing more than 600 rounds expended (i.e. more than 125 rpg for four guns) to shoot down a fighter that one has to wonder whether the exact same placement for the four gun battery would have resulted in a much faster kill. I suppose so, but by same token I suspect the number of 3 kill+ encounters would have also fallen off due to running out of ammo faster.

Post D-Day I wonder how much more effective 4 x 20mm (or 6x) would have been in a Jug for CAS than the 8x .50 cal.

The primary reason for switching to 20mm as a result of Korea experience in air to air combat was more about the lack of effectiveness of the .50 caliber round at causing fire or rapid structural failure in rarified oxygen enriched air at 35-40,000 feet.

 

[davparlr]

The primary reason for switching to 20mm as a result of Korea experience in air to air combat was more about the lack of effectiveness of the .50 caliber round at causing fire or rapid structural failure in rarified oxygen enriched air at 35-40,000 feet.

Will anything burn at 35-40k ft? I remember from my cargo driving days that one of the methods of extinguishing a cargo fire was to depressurize and climb.

 

[Kryten]

personally dont like mixed armaments, varying ballistics dont make for concentration of fire, would much prefer 6x.50, or 4x20mm than combinations!

 

[Shortround6]

personally dont like mixed armaments, varying ballistics dont make for concentration of fire, would much prefer 6x.50, or 4x20mm than combinations!

Between the .50 cal and the 20mm Hispano there wasn't enough difference at practical air to air distances to make a difference. The two guns were withing a couple % of each other in muzzle velocity and while the .50 cal bullet had a better shape, the 20mm had more mass per unit of frontal area. Once you get beyond 600yds or so a difference does start to show up but few pilots had any business firing at over 600yds. Anybody who doubts this can look at this sighting-in and trajectory chart.

http://www.zenoswarbirdvideos.com/Images/P-38/38BSC.gif

Please note that other 12.7mm and other 20mm guns had widely different MVs and would have problems at shorter distances than the .US 50 and the Hispano.
The closer the distance the less of a problem.

 

[drgondog]

Will anything burn at 35-40k ft? I remember from my cargo driving days that one of the methods of extinguishing a cargo fire was to depressurize and climb.

Nope - but 'rapid structural failure' was more in the world od 20mm.

 

[ShVAK]

For bomber defence guns, 50 cal. No sense having slower 20mm guns against a fast fighter.

I don't know, a tail-mounted 20mm was mounted in some larger types with good results. The H8K2 "Emily," an otherwise big and unwieldy IJN flying boat with not much armor was a pretty formidable target with its all-around 20mm armament, much like the Short Sunderland was. At the very least a cannon mounted astern in say a B-17 or -24 would make some LW pilots think twice about getting too close.