British 1936-42 purchase options, logistics and export/import of military hardware

[Shortround6]

Some engines - both liquid cooled and air cooled - benefitted more, some benefited less. The FS Mercury engines of late 1930s vintage went from being good for 800 HP at 9000 ft (and 840 HP at 14000 ft) on 87 oct fuel to 990 HP at 9000 ft on the early 100 oct fuel - an almost 25% increase.

Basically, only the Merlins were better in the % of extra power due to 100 oct fuel in that time, thatm in case of Mk.III gained about 35% at ~9000 ft (970 HP vs. 1300).

The Mercury, for British engines, showed the best increase in power form better fuel.

Availability of the high-altitude models of engines does not mean that the low- or mid- altitude models are not made.
On the bombers, there is a lot of place to fit and streamline the intercoolers. So better start working on these, including the suitable gearing of both S/Cs, so the, at least, Welligtons and Hampdens can cruise well at 20000 ft instead at 15000 ft, with bomber Ensign-lookalike and Halifax (with Hercules) following suit.

A lot of things are trade-offs and in the case of twin engine British bombers there may be a number of problems trying to operate at higher altitudes. The Pegasus was never allowed to use the higher levels of boost that the Mercury was. A bit higher yes, about 1 to 1.25lb of extra boost. The Pegasus XVIII was rated at 885hp at 15,500ft at 5lbs and 965hp at 13,000ft at 6.75lbs using 100/130. Now about 1/2 of the change is due to the 2500ft change in altitude.
Adding several hundred pounds of extra supercharger and intercooler/duct to the the medium bombers is going cut into the performance no matter how streamline you make it. Are you willing to cut into fuel or bomb load to carry the bigger supercharging system? There is going to be some improvement in performance. The question is how much and at what cost.

As noted by the users of the Mercury and the 100 oct fuel, there was a lot of stretch wrt. the engine strength.

In the Mercury yes, in the Pegasus it does not appear so. Actual problem may have been in the crankshaft? The longer stroke may have stressed the crankshaft more? Or they may have been a cooling problem. Adding an extra 1 in of fins at the bottom of the cylinder which is the coolest part of the cylinder may have meant the Pegasus had a problem with higher power. Taurus had cooling problems and the Hercules was never ending saga of trying to keep the cylinders and cylinder head cool. They did it but there were a number of cylinder and cylinder head redesigns to allow for more power. For the Hercules this was paralleled by the increase in allowable boost pressures.

Appeal of the more refined superchargers is that they use less engine power to provide the same boost at the chosen altitude, meaning there is more power left to the prop (with IHP remaining the same).

In some of these engines it wasn't worth the trouble. If an engine is only using 100hp to drive the supercharger going from 60% efficient supercharger to a 70% efficient supercharger is not even going to give you 10hp at the crankshaft on a 1000hp class engine. Or 20hp for a high gear ratio version. Now a more efficient supercharger will heat the air less and allow for more power because you can use higher boost.

Hence the suggestions to drop the Taurus in most of the what-if scenarios dealing with RAF for ww2.

The Taurus was an altogether bad decision by Bristol but it shows how sometimes designers and companies can fall into some holes in thinking. A very expensive/heavy small diameter (but low drag) engine will find acceptance over cheaper/lighter but higher drag engines in the market place???? The the hoped for 3300rpm never paned out which hurt power when the production engines stayed at 3100rpm.

High boost is not the only metric of the engine quality.

It is not but Bristol with sleeve valves had problems with BMEP that poppet valve engines did not. Using boost pressure is a shortcut to judging either BMEP or other structural problems, not 100% reliable but an indicator.

Marginal engines don't achieve 25% power increase when going from 87 to the early 100 octane fuel.

Mercury was a good engine, however it was too small. The Pegasus had problems with the long stroke. For most of the 1930s it was OK but the high piston speed limited RPM.
Compared to the R-1820 that used a 175mm stroke the Mercury used a 165mm stroke and the Pegasus used a 190mm stroke.
Perseus had a triple whammy. Too small (Mercury size cylinders), RPM limit very close to the Mercury. Early sleeve valves that didn't allow for high boost, perhaps not a problem with 87 octane fuel.
Wright redid the crankshaft/crankcase to go from 2200rpm to 2350 rpm and they did it again to go to 2500rpm and they did it yet again to go to 2600rpm. They also changed the cylinder barrels and the cylinder heads every time. There was never a "just change the supercharger" model change, maybe Wright just built crappy superchargers?
Bristol, like a lot (all) of Britain had shortage of engineers/draftsmen. They could not go in a lot of different directions as once. Just like manufacturing any major change in R&D may mean decrease somewhere else. They also spread themselves too thin in the late 30s.

This becames the same speke as the long range Spitfire - if it is not the 100% equivalent of the P-51D, then it is not worth it. To what I disagree 100% with.

There are things that are worthwhile to do even if they do not result in the best possible outcome. But some projects are not going to give a very good out come for investment.
If your resources (investment ability) are limited perhaps 2-3 good investments are better than 1 excellent one. And 2-3 good ones may beat 5-6 marginal ones.

 

[Shortround6]

There just weren't very many good supercharger designers in the 1930s. A good supercharger in the mid/late 30s was operating at a pressure ratio of about 2 to 1 or under.
There were exceptions both ways. But there was no store of unemployed (or under employed) supercharger designers to draw from. Even in 1938-39 Mercedes, despite their work on DB aircraft engines contracted with Porsche to design a two stage supercharger for their F 1 Grand Prix car and Porsche used roots superchargers. This used special racing fuel and at sea level gave a max of 2.31 ATA.

 

[Shortround6]

Getting back to the British army we can look at several things.
Infantry and small arms, Not ideal (P-51Ds) but much better than average for rifles and machine guns. Trying to shift to the P-51D standard is not going to gain much.
Mortars need work.
Artillery. British need to get into at least the P-40 Tomahawk level and not be stuck with Sopwith Camels/Sopwith Snipes. Artillery was supposed to be the real killer on the battle field, responsible for more causalities than everything else put together. British army went to war with mostly WW I leftovers. Granted they gave most of them pneumatic tires and brakes for towing by trucks instead of horses. The ONLY bright spot was the 25pdr and they were running late and had the usual British crappy ammo. More later.
Tanks. The glory/stars of the ground forces. But as we know, the British had quite a number of problems.
Light tanks, too many of them in mid/late 1930s. 500 or so might have been OK. 1600+ was obviously a bit much. The amount of effort devoted to the MK VII Tetrarch in 1937-40 was something British could not afford unless several other things were cut. A bespoke 12 cylinder flat engine (even if two 6 cylinder truck engines using a common crankshaft?) that only went into 177 tanks (after the cut in orders) just shows the problem. The Harry Hopkins may have been Vickers trying maximize profits on R&D but contributed nothing to the allied war effort.
The often debated "cruiser" tanks. British tank doctrine need a lot of work. The A 13s, for 1938-1940 were not bad tanks considering what everybody had (nobody had P-51Ds). Problem for the British was that they went either backwards or sideways with the Covenanter and the Crusader. And picking two tanks with different engines didn't help production, neither did modifying the the existing engine to fit into a smaller tank to suit a theoretical doctrine requirement. The Speed equal armor idea should have been trashed back in 1916 at Jutland. Back to the 2pdr argument later. I will note that the Cavalier tank with heavier armor but the 60 in turret ring and turret sized for a 6pdr/75mm gun but using the same engine/transmission as the Crusader was just under 60,000lbs. About 34% heavier than a MK III Crusader and about 79% heavier than A 13 MK II. British were using rather simple math when pricing tanks in the late 30s and were trying use a formula the estimated cost by weight. Heavy tanks cost more and the order numbers were going to be less. Faulty thinking/doctrine. A tank using 40mm armor basis is going to be lighter/cheaper than the Cavalier but if you want a 3 man turret with a bigger gun tan the 2pdr there was going to be sizeable increase in weight.
The Infantry tanks. After the start with the rather useless Maltida Is (makes the Fairey Battle look positively battleworthy in comparison) the British showed a decent effort (P-40C ? or P-36C? ) with the Matlida II. Excellent armor made up (sort of) for high cost, slow speed and less that Steller reliability. Only the fact that the Cruisers were even worse kept the Matilda somewhat out of the spot light. Lack of HE shells for the 2pdr hurt as did the lack of modern AP ammo. Combine that with the stupid aiming system/doctrine and the Armor really gets the credit for the Matilda's success.
Valentine, Private venture 'saves' the day. Smaller/cheaper infantry tank has very good armor and good reliability but it is now the summer of 1941, the last 6 months of the this period of time. As a tank the vehicle is slow, has poor vision and needs the MK III version to get a 3 man turret (very cramped).
The Churchill gets squeezed in here just to show the division of effort. The A20 was requested in Sept 1939. Insistence in thick armor meant they needed to keep the 2pdr gun to keep the whole project from getting to big/expensive but the first trial runs in June 1940 showed a number of problems. The A22 inherited the Bedford twin 6 engine and by dint of loaning draftsmen from the Mechanization Board to Vauxhall a pilot model of the A22 was ready in Nov 1940. They had ordered 500 tanks from the drawing board and the first 14 tanks were ready in June 1941, except, numerous defects with the early versions required a lot of reworking, numerous detail improvements of components and even Vauxhall engineers assigned to the first units to deploy the Churchill tanks. How much effort was devoted to the Churchill program in 1939-1942 that could have gone into a better Cruiser/medium tank in those years?
Too many different designs and not enough coherent thoughts/doctrine on actual use/requirements.
Cruiser tanks are supposed to run around miles behind the front lines with no HE shells or HE support (or much in the way of smoke?)
Infantry support/break though tanks have no HE or smoke (or only in 2 vehicles out of a 14-16 vehicle company?) and are depending on artillery support from several miles away.
Cruiser tanks may be out of range from towed artillery.
British light tanks have trouble dealing with armored cars.

Again, the British don't need P-51Ds for tanks. In 1939-42 they need Hurricanes/P-40s not Gloster Gauntlets/Hawker Demons.

 

[tomo pauk]

Adding several hundred pounds of extra supercharger and intercooler/duct to the the medium bombers is going cut into the performance no matter how streamline you make it. Are you willing to cut into fuel or bomb load to carry the bigger supercharging system? There is going to be some improvement in performance. The question is how much and at what cost.

No cost at all. Extra 10-15% power while paying 2-3% weight and increase is a feature, not a bug. See Whitley when the Merlin switch was made. See He 111 and Do 17.
Also see Welligton Mk.3 - a much better performer due to extra power vs. the Mk.1.

In some of these engines it wasn't worth the trouble. If an engine is only using 100hp to drive the supercharger going from 60% efficient supercharger to a 70% efficient supercharger is not even going to give you 10hp at the crankshaft on a 1000hp class engine. Or 20hp for a high gear ratio version. Now a more efficient supercharger will heat the air less and allow for more power because you can use higher boost.

BMW 801 gained some 15% extra power across the board when the excellent S/C from the 801E was mated to the rest of the engine of the 801D. Similar gain was achieved with the Hercules with the 100 series. Merlin 45 vs. Merlin XII - a gain of 20% over 10000 ft? In all cases, the gain was due both to the improved impeller and due to the application of the more streamlined, axial intake elbow.
Mercury and Pegasus were not just with the obsolete (no curved, let alone parabolic front part) impellers and obsolete (cluttered & squished) intake elbow, but also with impellers that had no shroud. So there is another thing to improve, meaning yet another few % power that can be gained.

But even a 10% power increase would've been worth it. in the late 1930s/very early 40's. Especially with Taurus out of the picture.

There just weren't very many good supercharger designers in the 1930s. A good supercharger in the mid/late 30s was operating at a pressure ratio of about 2 to 1 or under.

Seems like the radial engines were especially bad, wherever one looks at. BMW, Bramo, P&W, Bristol, G&R, Soviets, Japanese - nobody have had a S/C that had all of this (especially the last two were lacking):
- big enough and fast-turning enough for 15000 ft and greater operation altitude
- refined enough so it does not suck out extra power and not to heat the air or mixture too much
- a streamlined axial intake elbow

Bristol S/Cs were the biggest when compared to the engine displacement and power, while Wright were the only ones with the curved impeller blades? It took some time for the companies to improve on all these factors. Perhaps Tumansky and G&R were the 1st to do this in a good fashion with the M-88B and 14R, respectively?

Then we have the number of stages question - some 'radial' companies were making the 2-stage engines on trials basis for non-military purposes (Bristol, Piaggio) as well as for the military purposes (P&W). But it took until well into ww2 for the 1st such engines to power actual military A/C (by P&W), while the promising Hercules VIII went nowhere as far as it is about actual ww2 use.

 

[tomo pauk]

Tanks. The glory/stars of the ground forces. But as we know, the British had quite a number of problems.

Deciding that the future tanks need to be better in any regard than the ww1 tanks might've helped?
- Purpose of the tanks: to engage every ground/surface military and supporting asset owned by the enemy; what is beyond the ability of a tank, it needs to be tackled with (heavy) field artillery or with infantry; if artillery cannot reach it - that is not Army's job anyway unless the Army aircraft can reach it.
- Firepower is why the 'normal' tanks are bought. The ww1 6pdr is the low bar for the HE and AP performance, any new tank gun needs to beat this gun by at least some margin. Thus it is either a much improved 6pdr for the tanks, or the new compact 3in gun (not a howitzer of some kind). Add MGs to the taste.
- Tanks that can't carry these cannons (talk something lighter than 13 tons?) need a back-up light gun. That might be a 20 mm autocannon (possibly also used as an AA gun), barter with the French their 25mm gun, or perhaps have Vickers make a 1-shot gun that uses the 2pdr pom pom ammo. Same stuff for the light armored cars. If a HMG is chosen, it need to be a 2-gun high-elevation setup with ability to engage aircraft.
- Maneuverability: a combination of the good suspension, track size & design, engine and transmission. Tanks above 25 tons get a very good transmison and engine (Kestrel, Lion; even the Liberty can do the trick; perhaps a V6 spin off from the Condor diesel or Buzzard line?), tanks between 15 and 20 tons get the twin six-cyl commercial engine (there is a lot to choose from), while the tanks under 10 tons get a single 4- or 6-cyl commercial engine.
- Armor: get a lot of it on the expensive tanks. Pay the price in speed.

 

[Elan Vital]

Deciding that the future tanks need to be better in any regard than the ww1 tanks might've helped?
- Purpose of the tanks: to engage every ground/surface military and supporting asset owned by the enemy; what is beyond the ability of a tank, it needs to be tackled with (heavy) field artillery or with infantry; if artillery cannot reach it - that is not Army's job anyway unless the Army aircraft can reach it.
- Firepower is why the 'normal' tanks are bought. The ww1 6pdr is the low bar for the HE and AP performance, any new tank gun needs to beat this gun by at least some margin. Thus it is either a much improved 6pdr for the tanks, or the new compact 3in gun (not a howitzer of some kind). Add MGs to the taste.
- Tanks that can't carry these cannons (talk something lighter than 13 tons?) need a back-up light gun. That might be a 20 mm autocannon (possibly also used as an AA gun), barter with the French their 25mm gun, or perhaps have Vickers make a 1-shot gun that uses the 2pdr pom pom ammo. Same stuff for the light armored cars. If a HMG is chosen, it need to be a 2-gun high-elevation setup with ability to engage aircraft.
- Maneuverability: a combination of the good suspension, track size & design, engine and transmission. Tanks above 25 tons get a very good transmison and engine (Kestrel, Lion; even the Liberty can do the trick; perhaps a V6 spin off from the Condor diesel or Buzzard line?), tanks between 15 and 20 tons get the twin six-cyl commercial engine (there is a lot to choose from), while the tanks under 10 tons get a single 4- or 6-cyl commercial engine.
- Armor: get a lot of it on the expensive tanks. Pay the price in speed.

For what it's worth, when the French enquired the British about engines suitable for tanks in late 1939, they were given trial results of the Napier Lion which showed that it wouldn't work well (durably) at rpms below 2000 with a less-than-77-octane fuel. The British used 68 octane, the French had a 65 octane standard, the Germans used up to 74 octane. The US did use 80 octane but the British could obviously not plan for the very favourable fuel situation of the mid-war Wallies.

Improving the Lion to work properly on low octane fuel at useful power densities (better than the Liberty or 12-cylinder commercial engine derivatives) may not have been worthwhile, especially if there are other flaws coming from its aviation roots (for the B1 Bis' aviation engine, it was observed in 1939 that it did not like mineral oil and would have to use castor oil; what did Lion use given its 1920's aviation origins?). As Ricardo noted, it might not be a much more difficult effort to design a new dedicated engine which will:
- allow the use of a standard powerplant for tanks of a similar weight category (in excess of 15 tonnes where powerful commercial engines become rare), rather than the plethora of designs (Liberty, Meadows DAV, Bedford Twin-Six, twinned up Leyland/AEC on Matilda II, let alone the prototype petrol/diesels from 39-41 and the powerplants tested on A7 Medium Tank), and ideally a standard fuel ( decently low octane petrol or diesel)
- not have the logistical constraints of aviation or optimized truck engines (70+ octane rating gasoline, esp with alcohol additives, inconvenient lubricants and oil)
- not have the reliability/maintenance constraints of adapted engines (inconvenient access to spark plugs on many aviation engines, location of accessories)
- have a form factor, power density and structure allowing more compact powerplants and thus fewer constraints on tank design.

 

[z42]

Deciding that the future tanks need to be better in any regard than the ww1 tanks might've helped?
- Purpose of the tanks: to engage every ground/surface military and supporting asset owned by the enemy; what is beyond the ability of a tank, it needs to be tackled with (heavy) field artillery or with infantry; if artillery cannot reach it - that is not Army's job anyway unless the Army aircraft can reach it.
- Firepower is why the 'normal' tanks are bought. The ww1 6pdr is the low bar for the HE and AP performance, any new tank gun needs to beat this gun by at least some margin. Thus it is either a much improved 6pdr for the tanks, or the new compact 3in gun (not a howitzer of some kind). Add MGs to the taste.
- Tanks that can't carry these cannons (talk something lighter than 13 tons?) need a back-up light gun. That might be a 20 mm autocannon (possibly also used as an AA gun), barter with the French their 25mm gun, or perhaps have Vickers make a 1-shot gun that uses the 2pdr pom pom ammo. Same stuff for the light armored cars. If a HMG is chosen, it need to be a 2-gun high-elevation setup with ability to engage aircraft.
- Maneuverability: a combination of the good suspension, track size & design, engine and transmission. Tanks above 25 tons get a very good transmison and engine (Kestrel, Lion; even the Liberty can do the trick; perhaps a V6 spin off from the Condor diesel or Buzzard line?), tanks between 15 and 20 tons get the twin six-cyl commercial engine (there is a lot to choose from), while the tanks under 10 tons get a single 4- or 6-cyl commercial engine.
- Armor: get a lot of it on the expensive tanks. Pay the price in speed.

How much of this can we blame on

• Inexperience of designers?
• Desire by the Army to, under pre war budget pressure, to buy smaller and cheaper tanks rather than going big?
• Lacking doctrine? And can we realistically figure out a better doctrine without hard won battle experience?

Combine all three and you have a recipe for a debacle?

As for better guns, it seems highly optimistic you can mount a "new compact 3in (not a howitzer)" on a 13 ton tank, while retaining useful amounts of armor protection and mobility. If we look at the historical tanks equipped with medium velocity ~75mm guns, we seem to be talking about ~25 tons.

 

[tomo pauk]

How much of this can we blame on

• Inexperience of designers?
• Desire by the Army to, under pre war budget pressure, to buy smaller and cheaper tanks rather than going big?
• Lacking doctrine? And can we realistically figure out a better doctrine without hard won battle experience?

Combine all three and you have a recipe for a debacle?

• Some designers have had small experience. Some others - at Vickers - made the best-exporting new interwar tank (that British never adopted).
• British were buying, sorta, all tanks in the build-up towards the ww2 - light, medium weight, heavy weight.
• British have had the free & open inter-war period to experiment and test the ideas and hardware. Unfortunately, the Experimental Mechanized Force was cut short after just two years of running. So while indeed the experience won in the war is hard to beat, having additional 3-5 years of the EMF being active would've probably pointed to the more glaring issues, thus - hopefully - netting the armored force being better suited to the modern warfare.

As for better guns, it seems highly optimistic you can mount a "new compact 3in (not a howitzer)" on a 13 ton tank, while retaining useful amounts of armor protection and mobility. If we look at the historical tanks equipped with medium velocity ~75mm guns, we seem to be talking about ~25 tons.

British were outfitting the 16 ton Valentines with the medium-velocity 75mm guns. Not ideal fit, but it made for useful tanks.

 

[Shortround6]

Also see Welligton Mk.3 - a much better performer due to extra power vs. the Mk.1.

Amazing what you can do when you re-engineer the entire plane. The MK III was almost 4000lbs heavier tare weight than the MK IC. Max Gross around 6-8,000lbs heavier. Huge increases compared to the change in weight of the engines.

No cost at all. Extra 10-15% power while paying 2-3% weight and increase is a feature, not a bug. See Whitley when the Merlin switch was made. See He 111 and Do 17.

We had been discussing two stage superchargers. Now we are discussing engine swaps?

Then we have the number of stages question - some 'radial' companies were making the 2-stage engines on trials basis for non-military purposes

Bristol made it's 2 stage engine before they made a 2 speed supercharger. A two speed supercharger was an easier, cheaper improvement with a lot smaller impact on the airframes.
Just using an intercooler on a single stage supercharged engine was usually not considered worth the cost. I believe that the only production intercooled single stage supercharged engines to be used in production aircraft (at least until 1944/45) were certain models of Jumo 211.
Most everybody knew that the intercooler would increase performance of the engine. Most people thought that they were not worth cost in drag, weight and volume.

 

[tomo pauk]

Amazing what you can do when you re-engineer the entire plane. The MK III was almost 4000lbs heavier tare weight than the MK IC. Max Gross around 6-8,000lbs heavier. Huge increases compared to the change in weight of the engines.

The engines I've suggested would've necessitated a far lower increase of the tare weight.

We had been discussing two stage superchargers. Now we are discussing engine swaps?

We were discussing a lot. I was trying to point out that better engines were an improvement when retrofitted to the existing aircraft, despite these engines being often heavier.

Bristol made it's 2 stage engine before they made a 2 speed supercharger. A two speed supercharger was an easier, cheaper improvement with a lot smaller impact on the airframes.
Just using an intercooler on a single stage supercharged engine was usually not considered worth the cost. I believe that the only production intercooled single stage supercharged engines to be used in production aircraft (at least until 1944/45) were certain models of Jumo 211.
Most everybody knew that the intercooler would increase performance of the engine. Most people thought that they were not worth cost in drag, weight and volume.

Intercooler on a 1-stage supercharged radial of ww2 vintage was a no-go. On a 2-stage supercharged engine - be that a radial or a V12 - they were a net benefit, and were know to work in the years preceding the ww2. Same as the constant-speed propellers, or good flaps.
Air-to-air intercoolers were also pretty light.

Most people were not that into good superchargers either, and were not able to come out with the workable 2-stage superchargers even by 1945. Rarely the 2-stage superchargers were an instant and smashing success, but when that was the case, these were a great improvement over then-current 1-stage S/Cs.

 

[Shortround6]

A lot here.

- Purpose of the tanks: to engage every ground/surface military and supporting asset owned by the enemy; what is beyond the ability of a tank, it needs to be tackled with (heavy) field artillery or with infantry; if artillery cannot reach it - that is not Army's job anyway unless the Army aircraft can reach it.

The British, French, Germans and Soviets all believed that the tanks (at least some of them) should be able to travel beyond the range of heavy field artillery.
British really ran into the doctrine problem because they had very conflicting doctrines. There were no army aircraft (except Lysanders) because all the RAF bombers/strike aircraft were bombing enemy factories to stop resupply. RAF doctrine did not even cover German army supply routes. RAF believed that bombing the factories was the most effect way of stopping the supplies. The Army would just have to deal with whatever the Germans had stockpiled.
This may not have been what the RAF said in some budget meetings.
BEF went to France with 13 long range 6in guns. Yes 12 guns and one spare for 10 divisions. The max range for this left over WW I gun was 17,150 meters. Now since standard artillery practice is to try to keep your own guns out of range of at least the range of the enemy's more common artillery (say the German 10.5cm howitzers to be generous) that means the guns have be able to reach only about 5500 meters behind where the Gemans 10.5 howitzers are located.
Investing hundreds of thousands of pounds Stirling in "cruiser" tanks that can only go around 10km past the front lines and need 6in heavy guns to do it sure sounds like people are not talking to each other.

- Firepower is why the 'normal' tanks are bought. The ww1 6pdr is the low bar for the HE and AP performance, any new tank gun needs to beat this gun by at least some margin. Thus it is either a much improved 6pdr for the tanks, or the new compact 3in gun (not a howitzer of some kind). Add MGs to the taste.

Again it depends on the targets. A machine gun is effective against troops on the march, trucks, horses, wagons and rear command posts/HQs Rear area HQs were rarely dug in like front line HQs. They were out of artillery range.

- Tanks that can't carry these cannons (talk something lighter than 13 tons?) need a back-up light gun. That might be a 20 mm autocannon (possibly also used as an AA gun), barter with the French their 25mm gun, or perhaps have Vickers make a 1-shot gun that uses the 2pdr pom pom ammo. Same stuff for the light armored cars. If a HMG is chosen, it need to be a 2-gun high-elevation setup with ability to engage aircraft.

AA guns on tanks bring a lot of problems. In the 1930s everybody was still worried about gas. High angle guns are either outside like a LMG or require slots/openings in the turret that need gas proof sealing. The Pintle mounted LMG was both not very effective and exposed the crewman (often the commander) to bullets, bomb fragments.
In light tanks (like under 20 tons and in fact under 30 tons) using 20mm and larger guns as 2ndary weapons took up too much weight and volume. Only the French tried this post war with the AMX 30. British gave up on it after 6 of the first Centurion tanks.

If you don't have enough room in a Centurion what does have enough room?
You are trying not for a P-51D but a P-51H here.
Germans are about the only people that tried for the dual purpose 20mm + mg set up and that was in the armored cars. And they gave up a lot for it.

open topped turret with grenade screens are NOT tanks. Being vulnerable to rifles and machine guns at higher elevations is not a good idea for a tank.
If you want AA vehicles then build AA vehicles. Putting on guns that will point upwards may just make the men think they have AA defense when they don't.

- Maneuverability: a combination of the good suspension, track size & design, engine and transmission. Tanks above 25 tons get a very good transmison and engine (Kestrel, Lion; even the Liberty can do the trick; perhaps a V6 spin off from the Condor diesel or Buzzard line?), tanks between 15 and 20 tons get the twin six-cyl commercial engine (there is a lot to choose from), while the tanks under 10 tons get a single 4- or 6-cyl commercial engine.

Unfortunately for the British there was a real lack of 95hp and up commercial bus/truck engines. This was OK for the 6 ton light tanks, not so good for 10 ton tanks (unless you really liked the 10 ton French light tanks) and even for the 15 ton tanks. They had some but not enough. British need to decide on one or two engines, not the historic 3 to four before they even get to the Merlin. And how much mobility (speed) do they need if you are going to restrict ground pentation to the distance that can be covered by antique heavy artillery?
Doctrine was going in to many different directions.

- Armor: get a lot of it on the expensive tanks. Pay the price in speed.

Yes, the British could have used more armor. This should have been obvious as 30mm was pretty much the minimum standard against HE shells. The next rule of thumb was that a tank should be armored (at least on the front) to withstand it's own main gun. Here the early British cruisers failed miserably.

British were outfitting the 16 ton Valentines with the medium-velocity 75mm guns. Not ideal fit, but it made for useful tanks.

They were poor tanks, perhaps better than 2pdr armed tanks in 1943 but they had a number of major flaws. Poor Vision, low rate of fire/rate of engagement, slow, low ammo capacity, both for the main gun and for the co-ax gun. Since the Soviets were still building two man turret T-34s maybe they didn't look so bad?
BTW the Valentines with 6pr and 75mm guns were a bit over 18 long tons (41,000lbs).
Some of these heavy gunned small tanks were more SP guns with enclosed armor than actual tanks.
Sort of Stugs with rotating turrets.
When commanders mistook them for tanks they often suffered heavy casualties.

 

[Howard Gibson]

Some options for the aero engines:
- Basic Merlin is as almost as good as it gets, and it should've provided even better 'mileage' if it is not wasted in many hundreds of irrelevant aircraft; having a surplus of Spitfires means that Hurricane does not need the heart transplant in 1940 thus leaving the Merlin XX for the Spitfire for BoB. No Exe, no Peregrine. RR can act even earlier with the 2-stage supercharging, that was known to work with V engines years before ww2.
- Bristol 850-1100 HP radials: I'd rather see the much improved superchargers on the Mercury and Pegasus than the resources invested in the Taurus; the earlier Hercules can be gotten into service, the better. Bristol was big in the inter-war altitude records with what were basically 2-stage supercharged engines, so there is a lot to be gained if these systems are adopted for the military use.
- As noted by the fellow member earlier, having Napier to make a big honking V12 instead of the Sabre would've been a boon. The Dagger might've been an useful (if a bit expensive) engine for the bombed-up fighters, for example something that Army might find interesting.
- Taking a look in the American radials, like the R-1830 or the R-2600, should've produced the actual engines more likely than it was the case with trying to mimic the G&R 14 at Alvis, or the 'dog' engines at A-S. Alvis + P&W, and A-S + Wright anyone?

Aircraft powered by these engines will do better if the engines have a much improved layout of exhausts, as well as with the more modern fuel metering systems - the float-type carbs were really a handbrake to the engine abilities.

The Merlin_XXs went into Hurricanes because they fit. The Merlin_XX capable Spitfires did not reach service because they were in a panic to deal with Bf109Fs. The Spitfire_Vs had the new impeller without the two speed drive. This is post Battle of Britain.

The Napier Sabre's primary problem was the sleeve valves. I suppose that the H-24 made things more complex and expensive. I suspect that a V12 would have had a smaller frontal area. Note how the installation of the very big Centaurus did not affect the outline of the Tempest very much.

Most of the radial engined fighters that worked from mid-war on had big engines. The Bristol Hercules was marginally big enough, had the British been interested. Replacing the R2600 on the Hellcat with the R2800 was a good idea. I don't see the British accomplishing anything with a new aircraft built around the 28litre Wright and Pratt and Whitney radials, or the Bristol Taurus for that matter.

According to By Jupiter, by Bill Gunston, they were ready to manufacture Centauruses here in Canada. It is too bad nobody jumped on the opportunity. There is no way this makes the pre-war timeline.

 

[Shortround6]

According to By Jupiter, by Bill Gunston, they were ready to manufacture Centauruses here in Canada. It is too bad nobody jumped on the opportunity. There is no way this makes the pre-war timeline.

Perhaps they were ready to start construction of a factory to begin manufacture of the Centaurus in 1940. Getting any production Centaurus engines before 1942 seems doubtful.
Production of the sleeve valve engines was a little more difficult than than some people wanted to believe.
I would also say that with the US suppling most (almost all?) of the machine tools for any Canadian Factories in 1940, with the change in US priorities in the 2nd half of the 1940 the supply of US machine tools going to Canada was also going to change. Not stop but US factories are going to get some of the machinery first.

 

[Shortround6]

Britain did not have enough money/resources to get even most of what they wanted.
the BEF in France had only the above mentioned 13 6in guns and
13 8in howitzers (12 active and 1 spare) 10,430 meter range.
16 60pdr (5in) guns with 3 spares. 13,800 meters.
176 6in Howitzers with 45 in reserve. 10,430 meters range.

after that they were down to the 18/25lbs and 4.5in Howitzers (6040 meters).
Long range may have been in the British Army's vocabulary but it was not in the Army's capability and it would not be for several years.
The British 4.5in guns were not that great even when they showed up. (Cheap shells with low HE, what a surprise)
The 5.5in guns don't show up until 1942.

British "army air" disappeared after France 1940 and didn't re-appear until quite a period of time in NA and it was done by lower level officers and not the high level officers that gave the orders from above and actually ordered gear

British could have done a lot of things better if they had actually come up with an overall doctrine and not had a number of doctrines in conflict with each other and were more geared to furthering their own future agenda's than actually co-operating with each other and getting actual combat results.

 

[z42]

A lot here.

The British, French, Germans and Soviets all believed that the tanks (at least some of them) should be able to travel beyond the range of heavy field artillery.
British really ran into the doctrine problem because they had very conflicting doctrines. There were no army aircraft (except Lysanders) because all the RAF bombers/strike aircraft were bombing enemy factories to stop resupply. RAF doctrine did not even cover German army supply routes. RAF believed that bombing the factories was the most effect way of stopping the supplies. The Army would just have to deal with whatever the Germans had stockpiled.
This may not have been what the RAF said in some budget meetings.
BEF went to France with 13 long range 6in guns. Yes 12 guns and one spare for 10 divisions. The max range for this left over WW I gun was 17,150 meters. Now since standard artillery practice is to try to keep your own guns out of range of at least the range of the enemy's more common artillery (say the German 10.5cm howitzers to be generous) that means the guns have be able to reach only about 5500 meters behind where the Gemans 10.5 howitzers are located.
Investing hundreds of thousands of pounds Stirling in "cruiser" tanks that can only go around 10km past the front lines and need 6in heavy guns to do it sure sounds like people are not talking to each other.

It's slightly perplexing that they thought air power would be the artillery for the tanks. While SP artillery is more expensive than towed, surely it's still a lot cheaper than using aircraft.

Eventually the Brits got the 25pdr on a SP chassis, but that took until 1942, and the first iteration of the concept left a lot to be desired.

In light tanks (like under 20 tons and in fact under 30 tons) using 20mm and larger guns as 2ndary weapons took up too much weight and volume. Only the French tried this post war with the AMX 30. British gave up on it after 6 of the first Centurion tanks.

As I understood it, the suggestion was that light tanks would have an autocannon as main armament.

 

[tomo pauk]

The Merlin_XXs went into Hurricanes because they fit. The Merlin_XX capable Spitfires did not reach service because they were in a panic to deal with Bf109Fs. The Spitfire_Vs had the new impeller without the two speed drive. This is post Battle of Britain.

Merlin XX fitted on the Spitfires, too.
In 1940.

Panic was due to the Bf 109E having a 30-40 mph advantage over the Hurricane, thus Hurricane with Merlin XX. Merlin 45 inherited the impeller from the Mk.X (slightly improved vs. what the previous marks had) and elbow intake from the Merlin XX (much improved vs. the older marks).

Perhaps an interesting approach would've been that the Merlin XII gets the elbow intake designed for the XX from the get go? Might get them an engine almost as good as the Merlin 45, while no requirement for the 2-speed drive to be manufactured in the same time might have a lot of them produced vs. the limited production of the Merlin XX in 1940. Since the main recipient are the fighters, there is no major need to have the low speed gear on the Merlin.

Toss in a better fuel metering system (at least the pressure-injection carb) and low-drag exhausts (copy the idea from the Bf 109D from 1938) and one might touch 390 mph on a Spitfire and 340 on the Hurricane (mimicking the 8-gun Hurricane IIa), all for the late summer of 1940.
Granted, the better carbs and exhausts are feasible for 1939, too.

As I understood it, the suggestion was that light tanks would have an autocannon as main armament.

Yes.

 

[Shortround6]

The low drag exhausts may have been a good idea for a day fighter and this a what if and we can change things.

The original exhausts (after the simple ports in the side of the cowls in the prototypes) were also flame dampeners to aid in the nightfighter role.
The original spec called for a dual day/night fighter role. In the late 30s just the ability to take-off, fly and land at night without too high an accident rate qualified a fighter for night use.
The ability to actually fight at night was rather ignored.
The exhausts didn't work quite as well as desired leading to glare shields on some Hurricanes and a few Spitfires.

With hindsight we know that the Hurricane and Spitfire didn't make good nightfighters and burdening them with nightfighter equipment (exhausts for one) was not a good way to go.

 

[yulzari]

As to what might be achievable and useful for a tank we only have to look at the OTL Valentine. Yes you could do more but, for the first four years of the war, it was a perfectly serviceable tank. Reliable and reasonably well armoured although a bit slow.

The major fault is the gun not being dual purpose but the 6 Pounder could have been brought forward and was adequate in that period.

A few inches wider with a touch of overhang would allow a larger 3 man turret with the 6 Pounder and the same mount would carry the QF 75mm gun later on and make it easier to squeeze in a co axial machine gun.

Meadows had the capability and facilities to make a more powerful engine in the UK and Vauxhall could access General Motors for their smaller diesel too.

Overall not a super cool WoT fan machine but still an achievable sound tank as a national one type medium tank as the Commonwealth standard. Instructing industry to make just that type. Lord Nuffield can acquiesce or have his works nationalised and he can look at a new career in the Pioneer Corps.

Meanwhile its successor has plenty of time to be designed and well tested with Meteor power, Merrit gearbox and 17 Pounder gun. A 1943/4 Centurion.

The OTL Archer demonstrates how to build an SPG on the chassis for both a large AT gun or artillery although the artillery piece will need to be higher mounted to get the necessary elevation unlike in the OTL turret Bishop whose elevation was limited by the space inside the 25Pounder turret ring. Indeed there is no reason why the QF95mm could not also be brought forward to work on the same turret as the normal gun tank as an alternative choice.

This is a mix of what can be easily altered without major changes to what existed IOTL. What it does need which is very different is new doctrine and a single national tank board controlling the whole industry not dealing piecemeal with separate companies. Perhaps Vickers led as they have the practical experience.

 

[Shortround6]

Auto cannon for light armored vehicles gets tricky with 1930s technology.

Designers have a choice. Belt feed 20mm (or larger) auto cannon cannot change ammo types without great difficulty, Box magazines can change ammo easier (AP to HE) but don't work as well for AA. Now designing a turret that allows for high elevation requires a larger (read heavier) turret as the auto gun swings to elevate.
British experimental (?) AA tank

Ammo is outside, ability to change ammo types?
With a fast firing belt gun you can use belts of ammo of mixed types, alternate HE and AP.
Putting larger than 20mm guns inside armor gets tricky.
If the guns are outside we have an SP gun, not a tank.

 

[Shortround6]

As to what might be achievable and useful for a tank we only have to look at the OTL Valentine. Yes you could do more but, for the first four years of the war, it was a perfectly serviceable tank. Reliable and reasonably well armoured although a bit slow.

Citing the Valentine as perfectly serviceable tank for 4 years is both setting the bar very low and showing how bad the rest of the British tanks were and how faulty their doctrine was.

Good thing the Valentine is cheap because you need more of them. But needed to build more runs the total cost back up.

They were slow and at times could not flank the Germans in NA. They also could not avoid being flanked (or had to depend on other, faster tanks to do the flanking maneuvers)
Valentines, like a number of other British tanks, had very poor vision when locked down. And the 2 man turret versions suffered from this. Once you start shooting the commander was loader and if he pops his head out, he isn't loading the gun.
Valentines had limited ammo capacity. And with the bigger guns it was not only main gun ammo but machine gun ammo. I don't know were the sweet spot is but under 2000 rounds of co-ax gun ammo was not it. British Challenger tanks in Iraq went through over 4000 rounds of co-ax ammo in some engagements and had to withdraw. They were using the co-ax guns to suppress anti-tank missile teams and RPG teams. The need for decent co-ax guns and large ammo supply has not gone away.

Not buying 2pdr HE ammo for over 3 years was just stupid.
Not buying 6pdr HE ammo in quantity was also stupid. In 1942 they manufactured 2.5 million AP rounds and only 396,000 HE rounds. How many they issued?
One wonders how many German 50mm HE rounds were built and fired off in 1942?

German tanks had a better chance of success because the commander could see better. Both closed down and unbuttoned.
The British had jumped right over the 20-25mph speed range and either built somewhat reliable tanks that topped out 15mph or unreliable tanks that went 27-31mph.
The Germans built two different classes of 20-25 ton tanks but they were both 'universal' tanks. The MK III was supposed to handle just about everything and got smoke and HE support from the MK IV, but they were supposed to go the same speed and cross the same obstacles (or close) so they could support each other.
The British built too many different tanks that operated at different speeds and had different obstacle capabilities.

The British could have done a lot better than they did. There are reasons that there are books about "The Great Tank Scandal".

The British should not have to wait for the Merlin to get an tank that could beat the MK III & IV.