Boulton Paul Defiant Rationale

[XBe02Drvr]

The Defiant wasn't really a radical design, maybe just a high tech development of the Bristol Fighter.

Big shoes to fill, and the Defiant couldn't do it. The Bristol Fighter was a PERFORMER for its time AND it had a sting at both ends. Maybe the Mossie is a better analog? Big, powerful, fast, and maneuverable, only lacking a tail gun to be a perfect match.
Cheers,
Wes

 

[The Basket]

Oddly I read about Spitfires escorting Defiants to attack bombers. Cut the middle man out and get Spitfires attacking bombers!
Read some pilot saying Defiants were nice airplanes to fly. So that's a plus.
What the Defiant needed was to get rid of turret and gunner, be smaller and lighter and 8 guns in the wing. And the name changed to something like Spitfire. Could be onto a winner.

 

[Greyman]

I have no trouble with issuing a specification in 1935 to explore the "idea". The problems start creeping in with ordering hundreds of production examples when the Prototype had barely flown (without turret) and before firing trials were even conducted against towed targets.

I'm with you here, but I also try to keep in mind that this wasn't some academic exercise - and the powers that be were under the threat of possible Empire-ending HE, incendiary, and chemical doom from the air.

We quickly forget all of the off-the-drawing-board, hairbrained schemes that turned out great.

Maybe the Mossie is a better analog? Big, powerful, fast, and maneuverable, only lacking a tail gun to be a perfect match.

 

[pbehn]

Big shoes to fill, and the Defiant couldn't do it. The Bristol Fighter was a PERFORMER for its time AND it had a sting at both ends. Maybe the Mossie is a better analog? Big, powerful, fast, and maneuverable, only lacking a tail gun to be a perfect match.
Cheers,
Wes

I was just discussing the concept, no forward firing guns but a much more effective set up behind the pilot, I don't know if they knew how fast (slow) the defiant would actually be in service.

 

[Glider]

Big shoes to fill, and the Defiant couldn't do it. The Bristol Fighter was a PERFORMER for its time AND it had a sting at both ends. Maybe the Mossie is a better analog? Big, powerful, fast, and maneuverable, only lacking a tail gun to be a perfect match.
Cheers,
Wes

The comparison to the Bristol is interesting. When first introduced the Bristol was seen as a failure because losses were high. However when people looked into it, they realised that the pilots were trying to get into position for the rear gunners to fire. When tactics were changes and the pilots basically flew as a single seat fighters and left the gunners to use the opportunities that presented themselves was it a success.
This lesson was obviously forgotten with the Defiant as of course it was lacking the forward firing weapons

 

[buffnut453]

The comparison to the Bristol is interesting. When first introduced the Bristol was seen as a failure because losses were high. However when people looked into it, they realised that the pilots were trying to get into position for the rear gunners to fire. When tactics were changes and the pilots basically flew as a single seat fighters and left the gunners to use the opportunities that presented themselves was it a success.
This lesson was obviously forgotten with the Defiant as of course it was lacking the forward firing weapons

In fairness, the tactical situation faced by the Brisfit was entirely different to the one envisaged for the Defiant. The Brisfit was operating over enemy territory where encounters with German fighters were to be expected. The rationale for the Defiant was solely as a bomber destroyer because the UK mainland was, up until May 1940, beyond the range of Luftwaffe single-engine fighters. Ergo less of a "forgotten lesson" and more of a deliberate decision based on a tactical scenario that was entirely scuppered by the fall of France.

Now, I think it's fair to criticize the very narrow focus on destroying unescorted bombers...but, then again, how often do militaries the world over prepare to re-fight the last war only to find things have changed and so the soldiers, sailors and airmen have to adapt to an unexpected turn of events? The Defiant went too far in the other direction...the Air Ministry tried to second-guess the tactical environment of the future and came up with a one-trick bomber destroyer. That narrow train of thought was, sadly for the Daffy crews, never to eventuate and they found themselves up against arguably the best single-engine fighter in the world.

 

[stona]

Many of the answers are ignoring the fact that many felt in the mid 1930s that a single engine fighter would never be able to bring enough firepower to bear for long enough to destroy enemy bomber formations, even attacking in rigid formations (the numbered attacks of ADGB). It was this quest for firepower that led to the heavy armament of British S/E fighters. Eight machine guns was double the armament of many of the contemporary Bf 109s during the BoB, but many doubted that this would be enough.

What we now accept as an obvious standard, fixed guns in the wings and fuselage of S/E or T/E fighters, was no such thing in the mid 1930s.

The various other schemes, some never realised practically, were all efforts to bring enough firepower to bear on an enemy formation in order to break it and shoot the bombers down. The turret fighter, at the time, was probably the best of these schemes. It certainly wasn't the worst.

Presentism... something that many are guilty of, and not just in relation to WW2 aircraft

Cheers

Steve

 

[Tea Brewer]

I think the Defiant was a missed opportunity. I read years ago that it was designed with a provision for wing mounted guns, but the powers that be were slaves to their own dogma and rejected the proposal. In the same article it said that Boulton Paul offered the Defiant with solely wing-mounted guns as a single-seat fighter, but the decision makers said they had enough variants of single-seat fighters. Then of course they went ahead and bought the P-40 Warhawk, and its variants, that, on paper, the single-seat Defiant would have been a match for.

In WW1 the Bristol Fighter, the Brisfit, had both a forward and rearward mounted gun. When dogma declared that the observer's rear-mounted gun was to be the main armament, it was shot down like flies. When it was used as a conventional fighter with a sting-in-the-tail, it became one one of WW1's most successful fighters. The Defiant could have been WW2's Brisfit. It is mind-boggling that forward-firing variants of the Defiant were not even tested. Maybe they were, but I just haven't read about it.

It could also have been made a two-seat dive bomber in the manner of the Dauntless and thereby replaced the Blackburn Roc and Skua. Didn't Blackburn play a part in the design of the Defiant?

As a night fighter it seems logical in hindsight to have removed the turret, replace it with a forward-facing radar operator in the rear seat and wing-mounted cannon, even if these were mounted in pods. Such a move could also have been carried out for the electronic countermeasures the Defiant was employed in. I believe the turret was kept in this role, which limited the amount of jamming equipment the Defiant could carry. The turret was removed for target tug duties, so it seems reasonable to assume that it could have been removed for electronic-countermeasures. Maybe it was impossible to put radar and Mandrel equipment etc between the pilot and the rear seat? Does anyone know where the AI radar and Mandrel were installed in the Defiant? Was it in the cockpit?

It was said that the Defiant had limited range for Mandrel operations etc. I don't know if slipper tanks were tried, to increase the range. Spitfires ranged across all of Germany on reconnaissance missions using purpose-built slipper tanks, so again it would seem logical, in hindsight, to have fitted them to the Defiant.

The turret was very sophisticated. The streamlining fairings automatically retracted as the turret rotated. This can be seen on Youtube, in contemporary wartime propaganda films, one such is here
View: https://www.youtube.com/watch?v=ce9My4IKydo


Also, reportedly, the guns were electronically prevented from firing when pointing at any part of the airframe.

 

[stona]

The Defiant was never intended to have forward firing armament in the wings. Whoever wrote the article saying that it did is, frankly, mistaken. Boulton Paul could not have 'offered' the Defiant as a single seat fighter with fixed armament because that was not the specification it was built to. One of the main reasons they were offered and accepted the contract was because they already had the rights to the French SAMM turret on which the Defiant's was based.

The specification for the Defiant came after the failure of that for other multi seat turret fighters resulting from initiatives by Maund and Ellington.

The turret fighter that would eventually become the Defiant was proposed by Harris (yes, that Harris) when he was the Deputy Director of Operations and Intelligence (DDOI) in 1934. He proposed a new single engine two seat fighter to be included in the 1935 Experimental Aircraft Programme. This was agreed with the number F.9/35.
The Air Staff Requirement called for an aircraft which

"can bring fire to bear from a moveable battery of at least four machine guns over the upper hemisphere...; thus conferring on it the ability to attack from below and behind, below and in front, or on the flank of an enemy formation, at the same time enabling the batteries of all fighters to be trained on to the target simultaneously while in formation."

Fixed forward firing guns were specifically excluded, on the grounds that it was

"undesirable to split the armament."

It was also undesirable to have the pilot do anything but keep formation and it was considered dangerous for him to be aiming guns.

There were those who had argued for fixed forward armament. Even some of the strange ideas that had emerged from the Novel Fighter competition usually had some fixed forward firing armament. As early as 1933 Peirse (yes, that Peirse) had argued for a design not only with two fixed forward firing guns, but with a turret of four guns which could support them. This needed a two-engine design to avoid shooting off the propeller, so was not applicable to F.9/35.
The F.9/35 Defiant was not to receive a fixed forward firing armament, nor was it ever part of the Air Ministry specification to which it was built.

Cheers

Steve

 

[buffnut453]

There are 2 other key problems with having wing guns AND a turret in a Defiant:

1. There's literally nowhere to put fuel, therefore range would be abysmally short.
2. The extra weight of, say, 4 forward firing guns and ammo would further hurt the already less-than-stellar flight performance of the Daffy, making it even less manoeuverable and impacting climb, ceiling and top speed.

As Stona points out, including wing guns was never part of the spec.

 

[tomo pauk]

Many of the answers are ignoring the fact that many felt in the mid 1930s that a single engine fighter would never be able to bring enough firepower to bear for long enough to destroy enemy bomber formations, even attacking in rigid formations (the numbered attacks of ADGB). It was this quest for firepower that led to the heavy armament of British S/E fighters. Eight machine guns was double the armament of many of the contemporary Bf 109s during the BoB, but many doubted that this would be enough.

What we now accept as an obvious standard, fixed guns in the wings and fuselage of S/E or T/E fighters, was no such thing in the mid 1930s.

The various other schemes, some never realised practically, were all efforts to bring enough firepower to bear on an enemy formation in order to break it and shoot the bombers down. The turret fighter, at the time, was probably the best of these schemes. It certainly wasn't the worst.
...

Seems like that many also forgotten that airborne cannons were developed and used in air combat in days of ww1. Thus opting to be blind to series of cannons in production from 1920s by, not only, Oerlikon, and avoiding a possibility to have 2 bigger or 4 small cannons installed on the Hurricane and Spitfire from day one.
Eight LMGs was about equal of what most of the Bf 109s carried during the BoB.

I think the Defiant was a missed opportunity.
....
I don't know if slipper tanks were tried, to increase the range. Spitfires ranged across all of Germany on reconnaissance missions using purpose-built slipper tanks, so again it would seem logical, in hindsight, to have fitted them to the Defiant.

Slipper tanks, that go under belly in Spitfire-style, would've been blocking fresh air entering the cooler.
Defiant was not a missed opportunity, tooling up Boulton-Paul to make Spitfires instead would've brought advantage to the Allied war cause. Also leaves a number of Merlin XXs so Spitfire III can go ahead.

There are 2 other key problems with having wing guns AND a turret in a Defiant:

1. There's literally nowhere to put fuel, therefore range would be abysmally short.
2. The extra weight of, say, 4 forward firing guns and ammo would further hurt the already less-than-stellar flight performance of the Daffy, making it even less manoeuverable and impacting climb, ceiling and top speed.

As Stona points out, including wing guns was never part of the spec.

Since new fuel tanks were added in the Defiant Mk.II wings, there was certainly space left vs. Defiant I. The new fuel also impacted performance.

 

[GrauGeist]

The concept of the "turret fighter" was not unique to the Defiant, as Hawker's Hotspur was also submitted in response to the Air Ministry's F.9/35 Specification.

There was also Blackburn's Roc, that was developed from the Skua for the FAA as a turret fighter.

And there was even the Soviet's MAI Sh-Tandem that was intended to be a combination fighter, ground attack and light bomber.

The warfare ideaologies of the 1930's were born from lessons of WWI coupled with up and coming technologies that provided new avenues for weapon systems. A great many of those concepts (both hardware and tactics) of the 1930's were put to the test during WWII and were found to be lacking for many reasons.

While there were some systems that were able to adapt in order to prove successful, there's a very long list of one's that didn't.

 

[stona]

"Seems like that many also forgotten that airborne cannons were developed and used in air combat in days of ww1."

The British had reservations about the legality of cannon armament in the 1930s.

The Chief of the Air Staff (Ellington) saw the proposed COW gun fighter alternatives to F.10/35 when he approved withdrawal of the specification in June 1935. His comment on them would have consequences. He minuted.

"We should however, be clear as to our attitude to smaller caliber guns than the C.O.W. If other powers are ignoring the St Petersburg Convention (?) [sic] in respect of the weight of explosive projectiles, are we to do the same?"

The Convention agreement was that explosives would not be used in projectiles which weighed less than 400 grams. It did not apply to the 1.5 pounder (700 gram) COW gun but certainly did to the 20mm and 23mm cannon being developed in France and Switzerland. The British tended to honour Treaties and Conventions to which they were signatories, at least when practical, and such weapons were illegal. It was only in 1935, with Ellington's apparent willingness to ignore the Convention, that the RAF started to consider armament such as the French Hispano gun, designed specifically to be mounted on an aircraft engine.

When a new version of F.10/35 was proposed Sorley dropped the earlier proposals for the use of the COW gun and referred to an Operational Requirements' review of fighter armament which "advocated that we should develop a multi cannon armament".
To cut a long story short, an Air Staff Requirement was sent to the aircraft industry on 1st February 1936 as Appendix B of the future specification F.37/35 (amended from F.10/35) for a fighter with sufficient (at least four) 20mm guns, to give a decisive result at longer ranges than would a machine gun.

All this was far too late for the Defiant, which had the specified battery of machine guns. There was some talk of equipping the turret with cannon, but that's another story and anyway came to nothing.

Cheers

Steve

 

[yulzari]

I am always impressed with the 20/20 hindsight of commentaries upon the Defiant. Trials at the time of concept suggested that a 300mph fighter attacking a 250mph bomber would have such a short time of firing that it was unlikely to bring the bomber down. One response was for fitting 8 guns to throw more at the target in the short time available. Escorting German fighters were no expected to be able to escort German bombers if they flew from Germany. The Defiant turret took 4 guns that could fire upon the target for far longer than a single seat fighter could as it could formate upon the bomber/s swapping rate of fire for duration of fire. The bomber would likely receive more hits from the Defiant. Their other response was 4x20mm drum fed cannon (Whirlwind). The Defiant proved to be up to the job it was designed for.

Instead of pointing and laughing at the RAF planners they should be congratulated for their willingness to address the issues of high speed combat. Really putting 8 and then 12 machine guns in the wings of a single engined fighter was far more of a crude response to the brief engagement time than a sophisticated turret bomber destroyer or using 4x20mm cannon. They took bold and leading edge choices.

As it turned out the assumptions did not match events that unfolded but they were not to know at the time.

 

[tomo pauk]

"Seems like that many also forgotten that airborne cannons were developed and used in air combat in days of ww1."

The British had reservations about the legality of cannon armament in the 1930s.

The Chief of the Air Staff (Ellington) saw the proposed COW gun fighter alternatives to F.10/35 when he approved withdrawal of the specification in June 1935. His comment on them would have consequences. He minuted.

"We should however, be clear as to our attitude to smaller caliber guns than the C.O.W. If other powers are ignoring the St Petersburg Convention (?) [sic] in respect of the weight of explosive projectiles, are we to do the same?"

The Convention agreement was that explosives would not be used in projectiles which weighed less than 400 grams. It did not apply to the 1.5 pounder (700 gram) COW gun but certainly did to the 20mm and 23mm cannon being developed in France and Switzerland. The British tended to honour Treaties and Conventions to which they were signatories, at least when practical, and such weapons were illegal. It was only in 1935, with Ellington's apparent willingness to ignore the Convention, that the RAF started to consider armament such as the French Hispano gun, designed specifically to be mounted on an aircraft engine.

Hispano gun was not specifically designed to be mounted on an aircraft engine - British government bought the license for the gun despite there being no engines in the UK suitable to carry it that way. French installed two Hispanos in the wings of Bloch fighters, and even used it as a flexible defensive weapon.
British have had no problems in designing 25.4 mm (1 inch) cannon already in ww1 for air combat, certainly firig an under-400 gram projectile. Germany used 2 cm already by ww1 both for air fighting and AAA. French were using Swiss 20 mm cannons aboard their fighters in 1935. So there was plenty of precendents, home and abroad.
Considering the Hispano (in development) instead of Oerlikons (several mature cannons) in 1935 was a mistake, meaning no effective cannons for the 1st two war years.

I am always impressed with the 20/20 hindsight of commentaries upon the Defiant. Trials at the time of concept suggested that a 300mph fighter attacking a 250mph bomber would have such a short time of firing that it was unlikely to bring the bomber down. One response was for fitting 8 guns to throw more at the target in the short time available. Escorting German fighters were no expected to be able to escort German bombers if they flew from Germany. The Defiant turret took 4 guns that could fire upon the target for far longer than a single seat fighter could as it could formate upon the bomber/s swapping rate of fire for duration of fire. The bomber would likely receive more hits from the Defiant. Their other response was 4x20mm drum fed cannon (Whirlwind). The Defiant proved to be up to the job it was designed for.

Instead of pointing and laughing at the RAF planners they should be congratulated for their willingness to address the issues of high speed combat. Really putting 8 and then 12 machine guns in the wings of a single engined fighter was far more of a crude response to the brief engagement time than a sophisticated turret bomber destroyer or using 4x20mm cannon. They took bold and leading edge choices.

As it turned out the assumptions did not match events that unfolded but they were not to know at the time.

Usage of 4x20 mm was a good decision, if too late to matter. How much of trials was actually done, how serious they were?
A 300 mph fighter chasing a 250 mph bomber has a 50 mph speed difference, air forces were making kills with 40-80+ mph speed difference already in ww1, with far less capable guns and far less stable fighters. Is it that hard to slow down to 260 mph, = 10 mph difference?
Expecting that one's fighter will be happily hosing the enemy with stream of bullets, while bomber's gunners are expected to twiddle their thumbs, is what happens when googles are too much of rosy color. Expecting that Germans will not crush Belgium in a next war, chop North part of France, and base their fighters is another thing of rosy googles.

 

[stona]

"British have had no problems in designing 25.4 mm (1 inch) cannon already in ww1 for air combat, certainly firig an under-400 gram projectile."

When and where was that used? I am unaware of any 1" cannon, firing explosive ammunition, mounted on any operational British aircraft of WW1, but would welcome enlightenment.

Edit. The nearest I can think of is the 1.59" (40mm?) Vickers QF which fired a 540 gram shell, exempt from the Convention. This was cleared for use in aircraft in 1917. It was tested operationally, but was never adopted in numbers.

The British were looking at the HS 404 'moteur cannon', as used on the Dewoitine D.520 (and later the Morane-Saulnier M.S.406). At the time, replacing the COW gun in their specifications, they were looking at a centrally mounted installation, not something out on the wings. It was the absence of any British engine capable of utilising the French 'moteur cannon' concept that led to T/E designs being the first to mount cannons. The first cannon armed British fighters were in service in 1940, the Westland Whirlwind and Bristol Beaufighter, neither of which mounted cannon in the wings.

It is quite clear from a plethora of documents from the 1930s that the British had serious reservations about the legality of any ammunition that contravened the St Petersburg Convention.
It was the development of such systems by other powers that pushed them to consider them in 1935/6. If others were flaunting their treaty obligations then British reservations were overcome in the face of a looming European conflict.

Cheers

Steve

 

[tomo pauk]

When and where was that used? I am unaware of any 1" cannon, firing explosive ammunition, mounted on any operational British aircraft of WW1, but would welcome enlightenment.

Edit. The nearest I can think of is the 1.59" (40mm?) Vickers QF which fired a 540 gram shell, exempt from the Convention. This was cleared for use in aircraft in 1917. It was tested operationally, but was never adopted in numbers.

The 1in cannon was designed by Vickers in 1914, the British used only one example in ww1, sold the license to the Italians where it was produced as Vickers-Terni. Fiat-Revelli cannon, that used rimless cartridge, was designed to compete with it, a small batch was made, the project stopped when Vickers threatened them for breaching the patent.

The British were looking at the HS 404 'moteur cannon', as used on the Dewoitine D.520 (and later the Morane-Saulnier M.S.406). At the time, replacing the COW gun in their specifications, they were looking at a centrally mounted installation, not something out on the wings. It was the absence of any British engine capable of utilising the French 'moteur cannon' concept that led to T/E designs being the first to mount cannons. The first cannon armed British fighters were in service in 1940, the Westland Whirlwind and Bristol Beaufighter, neither of which mounted cannon in the wings.

It is quite clear from a plethora of documents from the 1930s that the British had serious reservations about the legality of any ammunition that contravened the St Petersburg Convention.
It was the development of such systems by other powers that pushed them to consider them in 1935/6. If others were flaunting their treaty obligations then British reservations were overcome in the face of a looming European conflict.
Cheers
Steve

I've just looked at the 'Table de tir pour le cannon automatique de 20 mm, 80 cal. HISPANO SUIZA TYPE H.S.S. 404', and expession 'moteur cannon' is novere mentioned. As above - HS 404s were used at just about any platform before ww2. British interest fot the HS 404 predates the D.520, even the MS.406.
Cannons of differnt types (but not the Hispano) were considered for the Spitfire at the time of Spit's development.
Unfortunately, the British didn't approached more aggresively to what they considered a breach of a convention already in the ww1 - basically, either sue the offending countries, or make their own guns in similar fashion. Or puchase license for those before 1930.

 

[yulzari]

I am always impressed with the 20/20 hindsight of commentaries upon the Defiant. Trials at the time of concept suggested that a 300mph fighter attacking a 250mph bomber would have such a short time of firing that it was unlikely to bring the bomber down. One response was for fitting 8 guns to throw more at the target in the short time available. Escorting German fighters were no expected to be able to escort German bombers if they flew from Germany. The Defiant turret took 4 guns that could fire upon the target for far longer than a single seat fighter could as it could formate upon the bomber/s swapping rate of fire for duration of fire. The bomber would likely receive more hits from the Defiant. Their other response was 4x20mm drum fed cannon (Whirlwind). The Defiant proved to be up to the job it was designed for.

Instead of pointing and laughing at the RAF planners they should be congratulated for their willingness to address the issues of high speed combat. Really putting 8 and then 12 machine guns in the wings of a single engined fighter was far more of a crude response to the brief engagement time than a sophisticated turret bomber destroyer or using 4x20mm cannon. They took bold and leading edge choices.

As it turned out the assumptions did not match events that unfolded but they were not to know at the time.

As an addenda to the above; the Air Ministry also dealt with the short firing time by introducing standard attack methods which involved queueing several single seat fighters in turn against a bomber. The 4 machine guns of the Defiant were not only chosen in the light of what could be practically mounted in a sensible turret but also at a time when the Gladiator was being ordered with the same armament as was the Skua which was a world leader in it's role at the time of introduction. The Defiant's Specification (F.9/35) was issued in April of 1935 and was the result of what was believed to be the state of things in 1934 when the Hawker Demon was entering service. It's immediate predecessor the Hawker Demon was well thought of by it's users at the time.

 

[stona]

"The 1in cannon was designed by Vickers in 1914, the British used only one example in ww1,..."

Which is,

a) why I've not heard of it in any British aircraft, and

b) what makes it irrelevant in this discussion.

In late April and May 1935 the Spitfire mock up was examined by various officers. A decision was taken, with Mitchell's approval, to increase the armament from four to eight machine guns, sacrificing the ability to carry a bomb and some tankage. There was no consideration of cannon.

The first mention of cannon comes in March 1936 with a NEW specification, F.37/35.
It was considered that the F.37/34 (Spitfire) could be 'adapted to meet the requirements of AM Specification F37/35 by modification of the wings to accommodate 4-20mm cannon...Alternatively, should a production order be placed for the F37/34 the provision of an alternative set of wings would enable one of the production machines to fulfil Specification F37/35.''
This is almost a year AFTER the decision to make the Spitfire an eight gun fighter had been taken. It is really suggesting an adaptation of the Spitfire to meet a new specification, even including alternative wings, rather than arming the prototype Spitfire with cannons


Cheers

Steve

 

[tomo pauk]

"The 1in cannon was designed by Vickers in 1914, the British used only one example in ww1,..."

Which is,

a) why I've not heard of it in any British aircraft, and

b) what makes it irrelevant in this discussion.

...

It is very relevant in this discussion since it shows, along the other cannons, that wepons firing explosive shells that were under 400 g were designed and produced by major powers during the very time the St Peterburg convention was in force.Thus British AM having a plausible way to introduce a 20mm cannon much before the HS 404 was even in the paper stage.

Also, for 1931, per Tony Williams (here):

The 1 inch automatic gun

Another possibility is revealed in an Ordnance Board note dated 25/11/31 concerning some correspondence with Vickers over a "1 inch automatic gun". In response to questions from the OB, Vickers responded with the following information:

1 - The estimated weight of the gun with a 60-calibre barrel will be 210 lb
2 - The type of action is the usual barrel recoil operated mechanism of the Vickers system with belt or link feed.
3 - The cooling arrangement is by water contained in a water jacket similar to the Vickers R.C. gun [rifle calibre]
4 - The gun will fire at the rate of 200 rounds per minute.
5 - The inboard length of the gun will be approximately 36 inches.

The types of ammunition proposed for this gun are:
- High explosive shell with sensitive fuze.
- Night Tracer projectile with internal night tracer.
While, if required, a hollow shot brought to weight could be supplied.

Naval gun, but still not complying with the Convention.