Did the British Air Ministry consider 0.55 in (14 mm) guns?

I'm reading about the Boys anti-tank rifle that fires a 0.55 in (14 mm) armour piercing round. Did the Air Ministry consider this calibre before adopting the 20mm cannon and US-spec 0.5 in?

There was also a 15 mm BESA machine gun round used on Guy and Humber armored cars.

Frog said:

There was also a 15 mm BESA machine gun round used on Guy and Humber armored cars.

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I thought the BESA was 7.92mm?

There was a 15 mm (0.59 in) BESA based on the Czechoslovakian ZB-60. About 3200 were manufactured (Wikipedia: Besa machine gun - Wikipedia).

I can think of several reasons why 14 or 15 mm guns weren't considered by the RAF, the first being that several 20 mm guns suitable for aircraft use were on offer during the mid-1930s, including one currently in aircraft use, e.g., the HS.404; there were few 14 or 15 mm aircraft guns in use (the only one I can think of is the Oerlikon MG/151). The HS.404 weighed less than the ZB-60[1], had a higher rate of fire (about 600 vs about 400), and fired a more powerful round.

Why would one consider a 15 mm gun when a 20 mm gun, better in most specifications[2], which was already in service, albeit with a non-allied, but not threatening, air force was available?


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1: The ZB-60 was the basis for the 15 mm BESA.
2: I don't know what the MTBF for either gun in comparable service conditions would be. Even if the BESA was better in ground service than the HS.404, it doesn't follow that it would have a better MTBF in aircraft service.

swampyankee said:

Why would one consider a 15 mm gun when a 20 mm gun, better in most specifications[2], which was already in service, albeit with a non-allied, but not threatening, air force was available?

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When development of the .55 Boys cartridge began in 1934 the RAF was some years away from fielding a 20mm cannon. And besides, the US fielded both .50 mg and 20mm cannons.

swampyankee said:

Why would one consider a 15 mm gun when a 20 mm gun, better in most specifications[2], which was already in service, albeit with a non-allied, but not threatening, air force was available?

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The RAF did a lot of testing for fighter guns in the thirties and the .303 was chosen due to being able to fire at a good rate plus
allowing fighters to have more guns fitted than many other countries fighters of the time.

The RAF also did testing against airframes rather than flat plate as a lot of rounds would be going through canvas or aluminium
and then tipping as they went into the innards of the target aircraft. Penetration capability at that stage wasn't an issue. More rounds inside the skin
gave a higher amount of damage - 8 x .303 - 160 rounds per second into the target compared by weight to three .5 at 40 rounds per second.
The .5 in comparison would have to have four times the damage capability.

The 20mm cannon was the next intended armament so as the quote here notes there wasn't much point bothering with an in between gun that
would need extensive modification to fire rimless rounds anyway. The BESA suited armoured vehicles nicely as the RAC had it's own
supply channel and the .303 was in high demand.

Admiral Beez said:

I'm reading about the Boys anti-tank rifle that fires a 0.55 in (14 mm) armour piercing round. Did the Air Ministry consider this calibre before adopting the 20mm cannon and US-spec 0.5 in?

.55 Boys - Wikipedia

en.wikipedia.org

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The Air Ministry considered it in 1940-41(?) and rejected it. RR was trying to branch out into firearms/armaments and the Air Ministry considered they had enough on their plate making aircraft engines.

What happened earlier I don't know, But there seem to have been no full automatic guns that fired the .55 in the 30s.

For questions regarding British ammo of under 20mm I strongly recommend this website.

It has 5 pages (1 general background and 4 for different types of ammo) just on the .55 cal Boys.

Like many 1930s cartridge's the bullet weight and velocity changed even for the same type of ammo. They were coming up with propellents that had better suitability for high velocity cartridges. Late 20s and early 30s cartridge/weapons trials were going to come up with different answers than 1940-41 trials.

The British already had the .5in Vickers cartridge and the space between it and the 20mm gets a little tricky to navigate. Something like the 15mm BESA is good hole puncher but that cartridge is so big it requires a gun the size of a 20mm Hispano to fire it. Vickers already had the .5 Vickers High Velocity round which was about 40mm longer in length than the short .5in round and about 20-21mm longer than the US .50. The propellents of the time did not allow full use of the extra case capacity, much like the US .50 cal gained about 340-380fps velocity in the 1940-41 US loadings over the 1920s/30s loadings. A 15% gain in velocity (and much greater gain in energy) makes a difference in trials.

The other problem was that regardless of the power of the cartridge, for aircraft use rate of fire was gaining in importance rather quickly. The small Browning fired about twice as fast as the Vickers .5in and the US .50 cal until 1940. The Vickers D gun (.5 Vickers High Velocity) fired about 1/4 as fast as the small Browning, longer bolt travel for one thing. A .55 machine gun may have been somewhere in the middle, perhaps closer to the 600rpm side than the 300rpm side?

RR gun chambered in US .50 cal 1940-41.

this 3-4 years after the 20mm Hispano was adopted. The .55in version may never have been completed?
Details are often contradictory, incomplete, or downright false (typos ?)

Admiral Beez said:

I'm reading about the Boys anti-tank rifle that fires a 0.55 in (14 mm) armour piercing round. Did the Air Ministry consider this calibre before adopting the 20mm cannon and US-spec 0.5 in?

.55 Boys - Wikipedia

en.wikipedia.org

Click to expand...

I might be mistaken, but the Boys Gun originally used a 13.2x99 Hotchkiss round and then after trials in March 1936 they decided to neck the round out to .55.

As such, I don't think there would have been a suitable automatic weapon available for the Boys 0.55 round. I also think the RAF had already decided to adopt the Hispano at this point. The first Hispanos began arriving in the UK for evaluation at the start of 1937, after notable delays.


If you want an alternative weapon in the .50 class, there's also the Vickers Class D. This has a 12.7x120mm cartridge and pushed out a round at ~3,040 fps. It was also a big (6 ft long), heavy (101 pounds) and slow firing (~350-450 rpm). With only very limited export success.

The Royal Navy reportedly tested it in the late 1920s. Why no-one thought of the round for the AT gun role is probably one of those very British mysteries, involving a lot of people boldly doing their own thing and not talking to other people.

Jabberwocky said:

I might be mistaken, but the Boys Gun originally used a 13.2x99 Hotchkiss round and then after trials in March 1936 they decided to neck the round out to .55.

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That was the same round as used by Belgium for their own build Hawker Hurricanes mounting x4 13.2mm FN Brownings.

yulzari said:

That was the same round as used by Belgium for their own build Hawker Hurricanes mounting x4 13.2mm FN Brownings.

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Now those were some interesting guns.

Somewhat lighter than the US version and faster firing too, with HE and incendiary rounds ready to go. The Swedes got a production line up and running in during the war, and not in the easiest of circumstances.

Jabberwocky said:

Now those were some interesting guns.

Somewhat lighter than the US version and faster firing too, with HE and incendiary rounds ready to go.

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Might depend on the actual facts and the criteria used.

Wiki says the FN gun weighed 54lbs with a 7.3lb barrel.
U.S. 1942 Manual says the M2 gun weighed 61lbs with a 10.2lb barrel.
Cutting the barrel weight helps to speed up the gun, but,,,,,,,,,,,,,,,,

Things we don't know.

Barrel life.
Not good in the 13.2mm Hotchkiss guns using the same ammo at a much lower rate of fire (450rpm)
The US .50 cal M2 had a pretty poor barrel life and next to nobody fired according to the manual. 1942 manual is for the new M2 ammo.
75 rounds (5.76 secs) in the first burst from a cold barrel. In a gun preheated by the engine (early P-40) the first burst was supposed to limited to 50 rounds (3.84 seconds).
Not bad on it's own. Problem starts with the follow up bursts, which are supposed to limited to 20 round burst per minute after a one minute cool down from the first burst and a one minute cool down between each follow up burst. There is supposed to be a 15 minute cool down period before firing a 50-75 round continuous burst.
Later in the war US guns got chrome plated bores and at some point (during the war or post war) they got Stelite liners barrel liners.

Reliability.
What was the acceptable rate for jams/stoppages per 1000 rounds fired.
Durability
What was the acceptable rate for broken minor parts per 1000 rounds fired.
What was the acceptable life for major parts or for the receiver. (British and Americans tended to over build guns. Not sure every receiver needed to last for dozens of barrel swaps).

It took a number of years for the US to come up with the M3 gun. But they were looking for no more than 5 jams/malfunctions per 1000 rounds and only one broken part per 1000 rounds. This is in a test stand at the factory/proving ground, what happened in service?

I don't know what the British criteria were and I don't know what the Belgian/Swedish criteria were. US may have screwed themselves with to many restrictions, one of which was that they were looking for a drop conversion parts kit for existing guns and they never got it. The US might have had 1200rpm guns in late 1942 or early 1943 if they had switched the requirements to a slightly modified receiver and bolt and accepted a few more jams per 1000 rounds and 2-3 broken parts per 1000 rounds.

Aside from the exploding bullets the 13.2mm ammo doesn't buy much.

Ammo......................................bullet weight.....................velocity
US old (1940) ammo.................46.8g..............................762ms
13.2mm............................................52g.................................790-800ms
US new (1941?) ammo...............46g.................................853ms.

Light barrels heat up faster than heavy barrels.
No idea what the British standards for jams/malfunctions/broken parts were in the 1930s.

Please note that the weight for the US M2 in the manual is for a bare gun. Mounts, external/remote triggers (electric or other mechanical) and remote cocking systems are extra, but would also have to be added to most guns.

Shortround6 said:

Aside from the exploding bullets the 13.2mm ammo doesn't buy much.

Ammo......................................bullet weight.....................velocity
US old (1940) ammo.................46.8g..............................762ms
13.2mm............................................52g.................................790-800ms
US new (1941?) ammo...............46g.................................853ms.

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Swedish ammunition data for their m/39 & m/39A:

AP (1939): 50.75 grams, 800 m/sec
HE-T (1939): 42 grams, 900 m/sec, filler of 3.2g of tetryl
AP HE I (1944): 46.75 grams, 815 m/sec, filler of 1.2g of HE and 0.8g of incendiary material.

It seems like a basic FMJ ball round (possibly a training round) and an AP-T round were also produced, but I can't find specifics for those.

Shortround6 said:

No idea what the British standards for jams/malfunctions/broken parts were in the 1930s.

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That was another reason for eight machine guns as one being jammed or whatever leaves you with seven to keep using.

As an aside, Boulton Paul proposed a turret armed with 50 cal MGs to the Air Ministry in 1940, but the firm was told by MAP that expediency was the key at the time and the firm was ordered to concentrate on producing turrets armed with 30 cal MGs to fit aircraft rolling off the production lines, notably in BP's case, the Halifax and US aircraft arriving in country, such as the Hudson and Ventura. The BP Type T turret armed with twin 50s never entered service on a British bomber but was sent to the USA in 1941, along with other examples of British turret designs and Sperry almost slavishly copied it to build what became the top turret of the B-17E, down to the electro-hydraulic working gear that BP employed for all its turrets. BP, Nash & Thompson, and Bristol eventually succeeded in getting 50 cal armed turrets onto British bombers late in the war. In 1943, trials with a 50 cal armed BP mid upper turret were carried out on a Lancaster at Farnborough and the Lancaster Mk.VII, when it entered service had a twin 50 cal Nash & Thompson rear turret, with a US-built Martin top turret, although it retained the N&T 30 cal armed nose turret. The Avro Lincoln, when it entered service was armed with 50 cal armament in the nose and tail and a 20 mm armed mid upper turret.

N&T FN.82 tail turret fitted to a Lancaster Mk.VII.

DSC_2859

Avro Lincoln armament: BP Type D tail turret.

BP Type D

BP Type F remotely operated nose turret. This was controlled from the glazing below the turret rather than an occupant within the turret.

BP Type F

nuuumannn said:

As an aside, Boulton Paul proposed a turret armed with 50 cal MGs to the Air Ministry in 1940, but the firm was told by MAP that expediency was the key at the time and the firm was ordered to concentrate on producing turrets armed with 30 cal MGs to fit aircraft rolling off the production lines, notably in BP's case, the Halifax and US aircraft arriving in country, such as the Hudson and Ventura. The BP Type T turret armed with twin 50s never entered service on a British bomber but was sent to the USA in 1941, along with other examples of British turret designs and Sperry almost slavishly copied it to build what became the top turret of the B-17E, down to the electro-hydraulic working gear that BP employed for all its turrets. BP, Nash & Thompson, and Bristol eventually succeeded in getting 50 cal armed turrets onto British bombers late in the war. In 1943, trials with a 50 cal armed BP mid upper turret were carried out on a Lancaster at Farnborough and the Lancaster Mk.VII, when it entered service had a twin 50 cal Nash & Thompson rear turret, with a US-built Martin top turret, although it retained the N&T 30 cal armed nose turret. The Avro Lincoln, when it entered service was armed with 50 cal armament in the nose and tail and a 20 mm armed mid upper turret.

N&T FN.82 tail turret fitted to a Lancaster Mk.VII.

View attachment 774001DSC_2859

Avro Lincoln armament: BP Type D tail turret.

View attachment 774002BP Type D

BP Type F remotely operated nose turret. This was controlled from the glazing below the turret rather than an occupant within the turret.

View attachment 774003BP Type F

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Lets not forget the Rose turret

The Sperry turret was not based on the Boulton Paul electrohydraulic design. It used the Vickers drive. The extraordinarily confused development and procurement of American turrets is presented in this Historical Study which I have posted in the past .
An interesting historical tidbit is that Lear Avia was awarded a contract to develop a turret drive. Lear Avia was founded by Bill Lear who later became famous for developing the much beloved 8 track tape as well creating the business jet.