British Army 'sanity options 2.0', 1935-43

I propose the above increases AND the upthread + above collating of independent infantry battalions and the conversion of MG battalions to regular infantry.

If we set a maximum annual increase target at ~12,000, for the purposes of argument, it might be possible to squeeze 4 additional battalions/year out of that, for 24 further over 6 years. In 1939, there were 15 Regular and 20 Territorial infantry battalions (or MG battalions) in Home Forces. That represents a further ‘source

MG bn conversion is a "zero" gain.

Assuming one MG bn per division, and reassign one MG plt to each of the nine battalions, BDE and Division staff and training cadre, 3 of 4 companies are gone.

Also the fourth company was for "other purposes", depending on theatre needs.

mgbn1940.jpg
mgbnmiddleeast1942.jpg
mgbn.jpg
 
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Arguably the single biggest thing the British Army needs to do is prepare its existing force for rapid expansion in the event of war from the leadership side of things
 
US fighter bombers were certainly the terror of allied PoWs trekking westwards. My stepdaughter’s grandfather was a CAM pilot taken prisoner in a ditching in the Channel and he was far more frightened by USAAF ground attacks than by the idea of being shot off a catapault in mid Atlantic in winter out of range of land. They shot up anyone moving in a line or group. He saw lines of civilian refugees and PoWs attacked on several occasions. Just as my mother witnessed the Luftwaffe doing in her trek south in France in 1940.
One thing I wonder about how a CAS doctrine would work in terms of the RAF earlier in the war - they tended to in OTL later on put a lot of stock in unguided rocket fire, which in 1944 saw an odd pattern of the RAF claiming much higher inflicted damage than the German records, which were copious at the unit level, indicated were true. And this happened on internal documents, not external ones for propaganda purposes. This is normal and expected, but not to the degree it happened.

I think the issue if anything is more in the way British CAS worked at the tactical level - there was far less cooperation with ground units or radio communication with something like Field Artillery Observation units, and the attacks tended to be ones of opportunity rather than a sort of "swarm on call" approach which every other major air power except the French, who were even more hopeless, frankly, at all stages of the war, utilized at some point.
 
Machine gun battalion conversion isn’t quite the zero gain.

In May 1940, the BEF had 3 such battalions at GHQ, 2 at I Corps; 2 with 1st Division, 1 with 2nd and 1 with 48th; 3 at II Corps; 2 with 3rd Division, 1 with 4th; 1 at III Corps, 1 with 42nd, 1 with 44th; 2 with 51st; and 1 with 23rd. 21 battalions including regular, trained men isn’t a good use of forces.

Under the model proposed, machine guns (be they old Vickers or a new GPMG) would be distributed within infantry units and the units converted to the MG battalions in the mid-late 1930s would remain as infantry. (https://vickersmg.blog/in-use/british-service/the-british-army/divisional-machine-gun-battalions/ ).

Replacing an MG platoon of 36 men with appropriate ‘indigenous’ forces within the infantry battalion corresponds to ~ 5000 men, which can be covered internally and through recruitment. I would note that not all of the 35 battalions were in the MG role.
 
In May 1940, the BEF had 3 such battalions at GHQ, 2 at I Corps; 2 with 1st Division, 1 with 2nd and 1 with 48th; 3 at II Corps; 2 with 3rd Division, 1 with 4th; 1 at III Corps, 1 with 42nd, 1 with 44th; 2 with 51st; and 1 with 23rd. 21 battalions including regular, trained men isn’t a good use of forces.

The "regular trained men" will still be needed for the bn MG plts of line battalions 😎

The bns do not have manning or training for MG plt and are generally under establishement.
(The "divisional" MG is effectively the pooling if Bn MG plts, and tasked.)


The MG bns at Army and Corps are formation troops. Reserve, guarding HQs and POWs. Converting a 650man MG BN to infantry requires another 150odd soldiers. These units are already tasked, and unavailable for other duties such as new divisions.
 
slipon-cheshire.jpg

This remained until the formation of Divisional Machine Gun Battalions in 1936 where guns were brigaded once again. The Cheshires were one of those Infantry Regiments converted to this new role.


2nd Battalion Cheshire Regt
This Battalion was an interesting one as it was never ‘mobilized’ but instead ’embodied’. It was part of the 55th Division initially but soon transferred to the 48th Division for administrative purposes but it was in reality part of the Corps Troops and did not wear divisional insignia. It went to France in January 1940 and took part in several actions there. After serious losses, including two complete companies, it returned to the UK at the end of May – via Bray Dunes.

It remained in the United Kingdom being a breeding ground for MG and Small Arms instructors and these were picked off by other Battalions and Regiments.
 
Part of Post 148.
From this, we can observe that there are some deployments which are Absolute Musts in the face of danger, namely Gibraltar and Malta and some which are Absolute Can Move, such as the Windies and China. There are also the 3-4 divisions worth of regular manpower in India.
Parts of Post 178.
2.) Yes, I am aware of the 55 Division Plan and the Indian component thereof; my ‘plan’ (not yet being as full formed as the @ one or your own) calls for a higher figure, rather than that particular compromise one. The Official History speaks ever so briefly and tantalisingly of other force plans at various stages, but there are some very clear limits in terms of materiel.
5.) I’m aware of the different form of the 7th and 8th; I will note that there were, in 1939, independent infantry battalions in Palestine, plus further ones and brigades in Egypt. My proposition is to:
I’ll have to think on the earliest junctures for conscription and the TA move, along with ideas for the Indian and Dominion pictures. That will then allow some appraisal of the required materiel et al.
Most of the little that I know about the Indian Army 1919-39 comes from Boris Mollo's book.

According to him the Indianisation of the officer corps began in 1919 when the Esher Committee on the future of the Indian Army anticipated the eventual removal of British troops from India and the replacement of British officers with Indian Army. This led to the Prince of Wale's Royal Military College being opened at Dehra Dun (to give a public-school type education to Indians considered suitable for commissioning) and the reservation of 20 places for Indians at the RMA Woolwich & the RMA Sandurst. At the same time 2 cavalry regimens and 6 infantry battalions were selected for Indianisation. Another cavalry regiment and another 3 infantry battalions were added later.

However, the Sandhurst experiment was not a success and as a result the Indian Military Academy at Dehra Dun was opened in 1932 which was commissioning 56 Indian officers a year by 1938. In October 1938, out of 4,000 officers of the Indian Army, 400 were Indian. By 1945 there were 8,000 out of 42,000.

That's close to verbatim from Page 162 of his book.

In the 1930s the number of British troops in India was cut from 75,000 to 57,000 and the Indian Army was cut from 159,000 to 140,000. However, the Army in India totalled 350,000, of which 61,000 were British troops, 205,000 regular Indian troops and 84,000 auxiliary troops including State Forces, NW Frontier units, Auxiliary Forces (India) and the Indian Territorial Force. The Army had fallen way behind in weapons and equipment, but manpower was less of a problem. The new Indian commissioned officers and the Indianisation of units meant that there was a strong nucleus of professional officer and NCOs on which to expand, and by 1945 India had 2.5 million men under arms.

That was a paragraph from Pages 164 & 165 of his book verbatim and the following is verbatim from Pages 163 & 164 of his book.

By 1938, it was apparent that the Indian Army required modernisation, and the growing threat of war introduced a note of urgency. In 1938-39 the Chatfield Committee recommended a programme of modernisation and mechanisation over the following five years. This was only just beginning to take effect when war broke out.

At the outbreak of war, the Army in India had three roles:
  1. A field army of four divisions and four cavalry brigades to guard against invasion by or through Afghanisatn.
  2. Frontier brigades to keep peace on the NW Frontier.
  3. Internal Security brigades to keep the peace within India.
Although there were no operational headquarters above Brigade, four district headquarters were designated as divisional headquarters on mobilisation. These were:

Rawalpindi District - 1st Indian Division​
Quetta District - 2nd Indian Division​
Meerut District - 3rd Indian Division​
Deccan District - 4th Indian Division​

Frontier brigades in Peshawar, Kohat and Waziristan districts were named after their respective territorial area (eg Landi Kotal Brigade). Internal security brigades had their own particular areas, eg Lahore Brigade Area. The field arm brigades were responsible for internal security in their respective areas.

The infantry and cavalry brigades, it was usual to have one British infantry battalion or cavalry regiment. All artillery was British, except for one regiment, the 1st Indian Field Regiment, formed in 1935, and the mountain batteries, normally allocated to the NW Frontier on attachment for particular operations.

****** ****** ****** ****** ****** ******​
Although the name of the thread is "British Army 'sanity options 2.0', 1935-43" the POD should be 1934 because that's when British rearmament began IOTL. Therefore, I think it's reasonable to start Chatfield's five-year programme of modernisation and mechanisation in 1934 instead of 1938 so it would have been completed by 1939 instead of 1943.

I think that little can be done to accelerate the Indianisation of the Indian Army's officer corps with a POD of 1934. The little that can be done being that more Indian artillery units could have been formed. That would assist your plan to upgrade the British 7th & 8th Infantry Divisions because the British field regiments that the extra Indian field regiments replaced would form their divisional artilleries. However, as you may not be aware, that would have been at the cost of a higher wages bill, because British troops in India were paid for by the Indian taxpayer and British troops in the rest of the World were paid for by the British taxpayer.
 
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4.) I’m all for the TA armoured division, but in concert with extra units outlined in 3.) above, there is also sufficient ‘spare battalions’ to rise above a cap of 5 divisions. I propose the above increases AND the upthread + above collating of independent infantry battalions and the conversion of MG battalions to regular infantry. That provides the extra needed for a rise from 5 to 8 regular infantry in the Home Army.

They would perhaps take the nomenclature of the Guards Division, 6th Infantry Division and 9th Infantry Division. With the returned 7th and 8th plus 1st and 2nd Armoured, that gives us 12 regular divisions to form the first part of a BEF, with plenty of spares.

I would not re-role the 2 TA to AA, but raise additional TA formations for that role in 1934-1939.
I think you'd be better off keeping the 7th & 8th in the Middle East and form them into a corps with the 7th Armoured Division and leave the 13th &`14th TA infantry divisions in the UK as reinforcements for the BEF. As it is you're sending 2 TA divisions trained for operations in Europe to the Middle East and 2 Regular divisions trained for operations in the Middle East to Europe. A corps of 3 regular divisions in the Middle East would be a useful instrument of diplomacy in the Middle East & Mediterranean theatre and I think the Regular divisions would have been more useful than 2 TA divs in the early stages of the war with Italy. Plus not swapping them saves shipping.

I've been looking through the notes I about the War Office plans for the TA in the late 1930s that I took from the National Archives more than a few years ago. The plan was actually for one cavalry division and a mobile division, but the headquarters for the latter wouldn't exist in peace. I intend to use them as the basis of a revised version of what I think should have been done.
 
Before I begin, I’d like to take the opportunity to thank you for your contributions to this thread and others like it over many years. The high standard of thought, research and development that goes into them is a true net gain to the knowledge base (and hopefully the wisdom) of the forum.
Thank you. Here's another contribution that came from the copies of the Army Estimates in the library of the National Army Museum.

Personnel Establishment of the Territorial Army 1933-34 to 1939-40.png

Notes
  • 1939-40 are the original Army Estimates for 1939-40, before the field force of the TA was doubled and before conscription was introduced, but the last one is IIRC because I haven't checked.
  • The Air Defence Troops (RA(b); RE(c); Royal Corps of Signals; RASC; RAMC; and RAOC)
  • (a) Including numbers for Coast Defence Troops, but excluding numbers with Air Defence Troops
  • (b) Excluding LAA Troops raised on a Territorial Army Reserve Basis.
  • (c) Including Infantry re-equipped as Searchlight Units.
  • In 1934 the TA 14 divisions each with 12 infantry battalions for a total of 148.
  • The reduced force of 114 infantry battalions was:
    • 90 for 9 ordinary divisions, each of which had one MG battalion and 9 rifle battalions in 3 brigades of 3 battalions.
    • 21 for 3 motorised divisions, each of which had one MG battalion and 6 motorised battalions in 2 brigades of 3 battalions.
    • 3 for the mobile division, that is one MG battalion and 2 motorised battalion.
 
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Some very interesting information; many thanks.

From it, I'll observe the following, working backwards:

Territorial Army
- Maintaining the 1934 TA first line infantry force of 148 battalions would be my ideal outcome
- Increasing Air Defence Troops gradually, involving the possible raising of new units/splitting of older ones into two, is one potential option to be explored. There are several years of 'static' growth in AD manpower that might bear further examination
- An aim would be for 9 infantry, 3 motorised and 2 mobile/armoured divisions for a minimum total of 101 divisional battalions, with the caveat that the overall organisational make up of some of those divisions will ideally need to change; 4 battalions of LoC troops for each 'corps element' of a future BEF, based of 3 regular and 3 Territorial 'corps' for a total of 24; and the remainder to be distributed for reinforcement of overseas garrisons or contingencies as necessary

Middle East
- Your idea regarding leaving the 7th and 8th in place with the 7th AD and the 10th Infantry Division makes very good sense. I'd hold 'TA 13' and 'TA 14' as a reserve separate from the 12 Infantry and 1-2 Mobile/Armoured Territorial Army divisions assigned to the BEF
- As you say, it saves shipping and training for different environments
- With the addition of further Indian/Imperial/Commonwealth forces, quite a lot can be accomplished

India
- Very interesting information. The number of deployable divisions fielded by the Indian Army needs to increase as far as practicable and possible
- I would propose setting as an aim 4 divisions within 3-6 months; and a further 4 at 12 months; and a further 4 at 16-18 months
- This compares to 10 divisions in @, in the form of 4th and 5th Divisions in 1939, 7th, 9th and 11th Divisions in 1940, 6th, 10th, 14th, 17th and 19th Divisions in 1941
- This would result in 4 divisions (possibly 1st, 2nd, 3rd and 4th Indian Divisions) being deployed to the Middle East/Egypt in 1939/40, with one or possible two going to the East African front and the other pair being assigned to the Western Desert Force/Desert Army/Whatever other label is used
- There would also be additional brigade sized forces for reinforcement of other areas in the Far East
- The Indian element would be part of the enlarged 'X British Empire Division Plan' in place of the 55 Division Plan. So far, we are up to 14 Regular Army (12 Britain and 1 mobilised in Egypt), 16 (14 I + 2 A) Territorial Army 1st Line and 12 TA 2nd Line for 42 British divisions as the aim. This compares to the 32 British divisions postulated in @ 1939


- This would make for an even 50 as an aspirational goal when the 8 AA divisions are added. I'm not sure specifically how many Canadian, Australian, New Zealand and South African divisions were incorporated in the @ 55 Division Plan
- It would be necessary to plan for the Malta garrison to be boosted to a division as soon as possible after the outbreak of a war
- It is likely that divisions would be still be converted or disbanded over the course of any (hopefully shortened) war, but this would be happening from the expanded base
- I haven't taken into account the need for further 'post mobilisation' Armoured Divisions, as that goes a tad beyond the scope of prewar rearmament; on top of 1st and 2nd and 7th from the Regular Army and 3rd and 4th from the TA, there could be up to another seven formed or converted. It really depends on what type of war eventuates
- I'd anticipate the possibility a further 4 AA divisions being established after mobilisation, similar to the @ figure of 12 in total. Alternately, the path taken in 1942 for conversion from Divisions to Groups could occur
 
4 battalions of LoC troops for each 'corps element' of a future BEF, based of 3 regular and 3 Territorial 'corps' for a total of 24; and the remainder to be distributed for reinforcement of overseas garrisons or contingencies as necessary

Sorry, 24 will not be enough 😢

LoC is not formation troops.
They are in addition to formation troops.

Also Pioneer bns are infantry. Not to be confused with Royal Pioneer Corps.

In the BEF, there is 4 bns of "garrison" infantry just to guard the LoC

HQ Lines of Communication British Expeditionary Force
Major-General Philip de Fonblanque

4th Battalion, Buffs (Royal East Kent Regiment)
14th Battalion, Royal Fusiliers
12th (Garrison) Battalion, Royal Warwickshire Regiment
4th Battalion, Border Regiment
1/5th Battalion, Sherwood Foresters

Corps troops had "on average" 2 MG BNS
Saar Force had 2MG &2 PN bns.

Army troops had even more, 9!!!
GHQ, British Expeditionary Force Headquarters Troops

GHQ-attached units

1st Battalion, Welsh Guards
7th Battalion, Cheshire Regiment (Machine-Guns)
14th Battalion, Royal Fusiliers (City of London Regiment) (company size) - garrison unit
8th Battalion, Middlesex Regiment (Duke of Cambridge's Own) (Machine-Guns)
9th Overseas Defence Battalion, West Yorkshire Regiment (Prince of Wales's Own) - garrison unit
6th (Argyllshire) Battalion, Argyll and Sutherland Highlanders (Princess Louises's Own) (Machine-Guns)
6th Battalion, King's Own Royal Regiment (Lancaster) (Pioneers)
7th Battalion, King's Own Royal Regiment (Lancaster) (Pioneers)
8th Battalion, King's Own Royal Regiment (Lancaster) (Pioneers)
6th Battalion, South Staffordshire Regiment (Pioneers)
 
I am aware of the deployments.

The @ BEF had 6 GHQ battalions + 4 in the pioneer role; 5 on LoC; I Corps 2 MG, II Corps 3 MG, III Corps 1 MG and Saar Force 2 MG and 2 Pioneer as you cited. That comes to 25.

As each corps' assignment of 4 battalions is more than all but Saar Force's assignment of the @ mix, it is ahead on that level. That leaves a need for at least 6 LoC battalions, 6 and 6 for GHQ reserve.

This isn't a major problem, given that, at this brainstorming phase, we are speaking of having a larger Regular Army, an enlarged 1st Line TA, an earlier embodiment/mobilisation of the 2nd Line TA and earlier conscription. If it comes down to it, the words 'for contingencies as necessary' can easily be read as entailing the deployment of appropriate TA battalions to that mission.

Rather than 138 Regular Army battalions in 1939, the aim should be for at least 162 (and preferable up to 192) as mentioned upthread, backed up by an absolute minimum of 148 first line Territorial Army battalions and at least 150 second line TA.
 
As each corps' assignment of 4 battalions is more than all but Saar Force's assignment of the @ mix, it is ahead on that level. That leaves a need for at least 6 LoC battalions, 6 and 6 for GHQ reserve.

Does that include the peudo corps in the NI, ME, Far East, East Africa, etc? 4 bns each as well?

Unfortunately, all these chew through numbers.

Conscription is not a quick solution either. Frustrating is the need to break up regular units to supply NCOs and Officers to new units, down skilling the regular battalions.
(Until they can train up their own new leaders, a catch 22!)
 
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No, just the BEF. As of 1940, there are not any corps deployed elsewhere other than the possible exception of Egypt.

Conscription is neither a quick solution nor a panacea, but it hasn’t been claimed to be one. It is one of four factors at play in a brainstorming process that is coming before a more fulsome idea/proposal.

There are limits to what can be done regarding the British Army with a 1934 kick off, but they aren’t so inherently egregious as to preclude any differing approaches to the size and structure of the force.

So far, the main substance of my approach has been to advocate small but steady increases to the Regular Army from 1934 onwards; not go down the path of converting infantry to specific MG bttns; tweak some deployments; reform the West India Regiment(s); not reduce the infantry strength and overall divisional strength of the TA; and to look beyond the 32/55 plan.

Nomisyrruc’s wonderful research has already given us the 14 TA infantry divisions and the proposed 1 mobile and 1 cavalry division, which opens things up a tad.
 
Part of the OP.
To start the ball rolling - keep the minimum new-development calibre of tank and anti-tank guns at 57mm, IOW don't go to 47 and 40 mm.
Part of Post 9.
An easy way for the Army to get a capable 6 pdr gun early enough would've been to piggy-back on the RN's 6 pdr 10 cwt program, whose series production started already in 1934. Should allow for all the British tanks and AT units to filed a capable, multi-purpose cannon before 1939, even if it is not 100% as capable hole-puncher as it was the OTL Army's 6 pdr (who cares anyway).
For what it's worth the specifications for what became the 2pd AT gun and Boyes AT rifle were issued in October 1934 which is close enough to the POD for the 6pdr AT gun and PIAT to be developed in their places. (IOTL the Vickers 2pdr was accepted in July 1936 and 812 were ordered.) I'm working with the POD in 1934 anyway because that's when Britain began to rearm IOTL.
 
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Part of the OP.

Part of Post 9.

For what it's worth the specifications for what became the 2pd AT gun and Boyes AT rifle were issued in October 1934 which is close enough to the POD for the 6pdr AT gun and PIAT to be developed in their places. (IOTL the Vickers 2pdr was accepted in July 1936 and 812 were ordered) I'm working with the POD in 1934 anyway because that's when Britain began to rearm IOTL.
I could see a case for picking the 57mm/6pounder as the next generation gun for introduction about 1940, but you then have to find an OK infantry AT gun as the 6 pounder was big and heavy.
The Soviet approach of copying the German 37mm but in 45mm is very appealing, if you could somehow copy the carriage and mount the 47 (hopefully with a better round than the standard Vickers medium one). Even the OTL rounds would be OK against most German tanks up to late 1940, but an improved shell (higher mv and then an APC round) would be good to end of 41 at least.
Otherwise, maybe copy the French approach with a 25mm / 1" calibre gun that is light, low and effective, and still useful when the 6 pounder enters service, although maybe leaving an uncomfortable period while the 6 pounders are being prepared for distribution.
Is there a case for a 25mm/1" being light and numerous enoigh to replace the Boys?
 
Part of Post 2.
Oh and Bofors guns, get them and share development with the RN, also the 3.7-inch AA, its got a far better fire control system than the RN's own HCAS, so share costs with them to develop that as a joint program.
Part of Post 7.
The problem with the 3.7 for the RN is that what the Navy (thinks it) needs isn't a dedicated heavy AA gun, it's a decent dual purpose medium gun - as opposed to the motley and diverse collection they actually had. They won't regard a 3.7 as packing enough punch for the anti surface role.
Part of Post 8.
I'm not talking about the gun because you're right, they'd want something with an anti-surface role, what I'm talking about is the 3.7's fire control system the army came up with, it was a fully tacheometric system and was more advanced than the HCAS the RN used at its time of introduction.
IOTL development of what became the 3.7in AA gun began in 1932 and 120 were ordered in November 1937. The Army chose to adopt a single version of the RN's twin 4.5in gun which was capable of 80 degrees of elevation. The book that I took that from said it wasn't surprising because cooperation between the Army's Director of Artillery and the RN's Director of Naval Ordnance was close.

I'm all for the Army and RN to standardising as much as possible to share costs and in the interests of standardisation to reduce production costs & reduce the logistical burden.

FWIW my choice is for the Army to adopt the RN's 4in AA gun instead of developing the 3.7in gun. That is, as long as it's not too heavy and not too big to meet the Army's weight and size requirements. Unfortunately, it may have been too big and too heavy for the Army because I think it would have adopted the 4in AA gun IOTL because as my source said cooperation between the ordnance branches of both services was close IOTL.

The RN developed a single 4.7in AA gun in the 1920s and I think the Army should have bought an improved version of that in place of the 4.5in AA gun. In turn the RN should have developed a family of twin DP mountings for the improved 4.7in AA gun instead of its OTL twin 4.5in and twin 5.25in DP mountings. Then the RN should adopt a navalised version of the Army's single 4.7in AA gun & mounting for its destroyers instead of the OTL single 4.5in gun & its DP mounting.
 
I could see a case for picking the 57mm/6pounder as the next generation gun for introduction about 1940, but you then have to find an OK infantry AT gun as the 6 pounder was big and heavy.
The Soviet approach of copying the German 37mm but in 45mm is very appealing, if you could somehow copy the carriage and mount the 47 (hopefully with a better round than the standard Vickers medium one). Even the OTL rounds would be OK against most German tanks up to late 1940, but an improved shell (higher mv and then an APC round) would be good to end of 41 at least.
Otherwise, maybe copy the French approach with a 25mm / 1" calibre gun that is light, low and effective, and still useful when the 6 pounder enters service, although maybe leaving an uncomfortable period while the 6 pounders are being prepared for distribution.
Is there a case for a 25mm/1" being light and numerous enough to replace the Boys?
AFAIK an infantry AT gun for the British Army is a non-requirement because IIRC the infantry didn't have it's own AT guns.

Instead, the infantry had the Boys AT rifle, which is why I suggested developing the PIAT in its place because AFIAK the technology existed or could have been developed in time for WWII with a POD of October 1934. An alternative might be a recoilless rife similar to the one that Dennis Burney developed later IOTL.

Edit 15:56 on 10.12.23.
The first sentence of this post is wrong. See Post 208 on Page 11 for more details.
 
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The RN's 4.7, especially the http://www.navweaps.com/Weapons/WNBR_47-50_mk11.php was a very powerful gun with more potent anti-surface capabilities than the USN's 5-inch 38. But the RN had 5 different 4.7-inch guns, each with their own caliber and different shells and mountings.

Post war the thought was that the 4.5-inch gun that was in development was a superior AA weapon but was not great for anti-destroyer work and would leave RN destroyers outgunned by other navies who were introducing 5-inch gunned ships and so the 4.7 was adopted but the RN kept iterating on it until they got to the 50cal version which was a VERY good anti-surface weapon and was a very powerful gun.

The problem wasn't the guns though, it was the mountings. Pre war the RN's AA doctrine was that a destroyer was simply too hard a target to hit by the main air threat of the time, level bombing, and that a torpedo carrying aircraft could be dealt with by the pom-pom. Destroyers would be manouvering aggressively to avoid bombs, so would be a poor platform for AA work a longer ranges and higher altitudes, and a DP mount is more complex and heavier than an anti-surface mount. The RN learning this lesson from the County class who's 8-inch turrets were designed from the onset to have a 70 degree elevation capability for HA fire against aircraft.

But these mounts were very troublesome in the early years and eventually the RN gave up on the idea and reduced elevation to a still impressive 50 degrees. The 8-inch mounts couldn't elevate or traverse enough but the deep deck wells needed for the guns to elevate up that high and fire made the turrets heavy, complex and awkward.

Going off this experience and their doctrine, the RN was quite happy to not have to worry about developing a DP mount for the heavy guns on their destroyers, as according to their own doctrine a DD would not be firing at targets at high altitude, and would only have to worry about low level threats. And when they did they were at best, adequate in terms of elevation and traverse rates, and the RN was never able to match the combo of the 5-inch Mk38 and the Mk37 fire control computer with its guns and the various marks of HCAS. There's a reason the converted D class cruiser HMS Delhi with her US 5-inch and Mk37 FCS was one of the best AA ships the RN had.

But here if the RN can in trade get the 3.7-inch gun's fire control system, its a fully tacheometric system from the get go and that makes it immediately superior to the in service HCAS the RN has, then this would, once iterated on at least allow the RN to get close to the Mk37.
 
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For what it's worth the specifications for what became the 2pd AT gun and Boyes AT rifle were issued in October 1934 which is close enough to the POD for the 6pdr AT gun and PIAT to be developed in their places.

Instead, the infantry had the Boys AT rifle, which is why I suggested developing the PIAT in its place because AFIAK the technology existed or could have been developed in time for WWII with a POD of October 1934. An alternative might be a recoilless rife similar to the one that Dennis Burney developed later IOTL.

Mohaupt independently developed and introduced the shaped-charge concept to
the U.S. Mohaupt’s earliest patent claimed a date of 9 November 1939. He used
liner cavity charges to design practical military devices ranging from rifle grenades,
to mortars, to 100-mm-diameter artillery projectiles. These devices were test fired
at the Swiss Army Proving Ground at Thun, at Mohaupt’s laboratory, and at the
French Naval Artillery Proving Ground at Gavre. A U.K. commission investigated
Mohaupt’s device and upon payment of a fee later witnessed test firings. The
British officers witnessing the tests surmised that Mohaupt was using the Neumann
principle and dropped negotiations because the price was too high [5].
As a result of the Mohaupt demonstration, however, the British reconsidered
whether the shaped-charge effect could be introduced into service munitions. The
early studies concentrated on a shaped-charge rifle grenade. After about a year’s
development, it was introduced into British Service in November 1940 as the No.
68 grenade. Thus, the British were equipped with the world’s first hollow-charge,
anti-tank rifle grenade [5
]. The British test results were sent to Washington and
negotiations began with Mohaupt. Before divulging any details, he demanded
$25,000, which the U.S. Army Ordnance Department did not want to spend. The
matter was dropped until Mohaupt came to Washington in 1940 and arranged for a
demonstration at Aberdeen Proving Ground (APG), MD. The U.S. Army and Navy
recommended acquisition of rights of the invention [5].
 
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