US light tanks derivatives: how would you do it?

[tomo pauk]

Since M3 medium, followed by M4 were to be 'proper' tanks, you can change/develop M3 light tank to be better suited for WW2 battlefield. Starting point can be US entrance in war; M3 is already in combat in N. Africa, using both US and UK/Commonwealth products for improvement. The 1st usage of new tanks/derivatives circa late summer of 1943 (invasion of Italian 'boot').
No Cold War guns, thankyou

 

[Shortround6]

A problem with "improved" light tanks is that they tend to turn into slightly small medium tanks unless much restraint is used.

http://i342.photobucket.com/albums/o431/Cowboy31a/pictureasforarmchair/T7E2_b.jpg

By they time they got done they hit 25 tons light and 29 tons and used some of the same engines as the M4 medium. It was finally canceled when it was decided it offered no advantages over the Sherman.

 

[Glider]

Have to agree, you either need an armoured car to do the job or you develop a small light tank such as the M24.

 

[tomo pauk]

... hence the "derivatives" keyword - feel free to 'make' a neat AFV to aid the Allied cause

 

[Shortround6]

Best "aid the Allied cause" would been to have developed a successor to the Sherman faster and skipped fooling around with light tanks. Yes they are useful for reconnaissance but the US made almost 9,000 M5 light tanks. That is a lot of recon vehicles.

Now are you looking for a "better" recon vehicle? 3 man crew instead of 4, lower height, faster, quieter, lower ground pressure for crossing muddy ground/snow?

Or are you looking for something better suited to slugging it out with MK IV German tanks and Stugs? Bigger gun, thicker armor?

 

[tomo pauk]

Something around APC, US Vespe, US Marder... US indeed produced AFVs that worked very well in these roles, but those were not available all places M3/M5 went. Sure enough, US Army wouldn't decline those, too

For inspiration, historical Stuart Pak.
Ingreadients are Stuart V supplied by UK for Yugoslav partisans (for their 1st Armored brigade, IIRC), captured 7,5cm Pak, work was done in late 1944 in shipyard in Šibenik, Croatia (60 km away from my town).
Stuart Flak also existed (quadruple 20mm Flak), and 15cm SiG was bolted on too.

 

[Shortround6]

Workshop conversions of small quantities (1-12) are one thing. Quantities like the US usually produced are another. The US probably tested most likely combinations:

http://mailer.fsu.edu/~akirk/tanks/UnitedStates/selfpropelledguns/usspg-M3-50cal.jpg

http://mailer.fsu.edu/~akirk/tanks/UnitedStates/selfpropelledguns/usspg-T18.jpg

http://mailer.fsu.edu/~akirk/tanks/UnitedStates/selfpropelledguns/usspg-T47orT17E1.jpg

http://mailer.fsu.edu/~akirk/tanks/UnitedStates/selfpropelledguns/usspg-M8A1.jpg

http://mailer.fsu.edu/~akirk/tanks/UnitedStates/selfpropelledguns/usspg-T56.jpg

http://mailer.fsu.edu/~akirk/tanks/UnitedStates/selfpropelledguns/usspg-T57-a.jpg

http://mailer.fsu.edu/~akirk/tanks/UnitedStates/selfpropelledguns/usspg-T27-81mm.jpg

http://mailer.fsu.edu/~akirk/tanks/UnitedStates/selfpropelledguns/usspg-T82.jpg

http://mailer.fsu.edu/~akirk/tanks/UnitedStates/selfpropelledguns/usspg-42-mortar-c.jpg

And using parts of of an M-3

http://mailer.fsu.edu/~akirk/tanks/UnitedStates/selfpropelledguns/usspg-45inch.jpg

http://mailer.fsu.edu/~akirk/tanks/UnitedStates/selfpropelledguns/usspg-T64-155.jpg

Of these one made it into production.

 

[tomo pauk]

Thanks for the links; the site is great well known.

After looking at what was tried, we still lack APC and SP ATG (3in).
The SP 105mm was designed in 1944 - too late to use production examples in combat; M7 Priest Sexton are available by then; it uses M3 howitzer that has lower MV than M2, M2 howitzer is in full production by the time M3 starts production (spring of 1943).

The placement of combat compartment hampers all 3 'versions'. Therefore, we copy Germans.
The Pz-II, Pz-38(t) and Pz-IV have had similar propulsion layout as US tanks - engine back, transmission on front. In converting tank hulls to 'geschützwagen', Germans have relocated engine in center of the hull, leaving the back of the hull free for guns, ammo and crew (minus the driver, of course). We will also extend the hull by 1ft, maybe 1.5ft, arriving at AFV as long as Wespe, or Marder III, but wider some 20cm.

 

[Shortround6]

The M-3 was too small to make a useful APC. See the Recce modifications with turret removed. needed 3 vehicles to transport a single squad isn't going to work. The other thing about Americans building some of these other versions is that they had halftracks out the wazoo.
Many of the functions could be done by halftrack conversions and done better. Half tracks provided the SP AA mounts, SP mortar mounts, SP 75 howitzer mounts, SP 105 howitzer and 75mm AT gun mounts.
In most cases they gave the guns crews more room to work and carried more ammo.

The Germans did a lot of those conversions because they had to. Lack of production capacity+ short development time. No or little MK III/IV production capacity to spare. When you get to the 105 Howitzers (Wespe) the use of too small a chassis starts to show. It carried 32 rounds of ammunition. Four every 4 gun armed vehicles there was a 5th without a gun that acted as an ammo carrier and spare chassis that a gun could be swapped into. The American M7 carried 69 rounds.

If you are talking about a "what if" in which the Americans had some bizarre reason only the M3 light chassis to work with then some of the vehicles make sense. With the M3/M4 chassis and the halftrack chassis available they don't.

 

[tomo pauk]

The M-3 was too small to make a useful APC. See the Recce modifications with turret removed. needed 3 vehicles to transport a single squad isn't going to work. The other thing about Americans building some of these other versions is that they had halftracks out the wazoo.

Asking from turret-less M3 to perform as proper APC is asking too much; asking from halftrack to be Armoured (the A from APC abbrewiation) is asking too much, too, as shown with usage of Cangaroos. Half-tracks, while better than trucks, can't compete with off-road capabilities of 90% of tanks.

Many of the functions could be done by halftrack conversions and done better. Half tracks provided the SP AA mounts, SP mortar mounts, SP 75 howitzer mounts, SP 105 howitzer and 75mm AT gun mounts.
In most cases they gave the guns crews more room to work and carried more ammo.

The half-tracks gave sterling job as platform for AAA, mortars, 75mm artillery. I did not ask from a M3 derivative to double in those roles, though.
The US half-tracks were not outfitted with 3in gun ( difference vs. 75mm is substantial in AT capabilities), while T-19 was judged to light for 105mm recoil, so 105mm was stripped from them eventually.
Again I'll admit, hull of M3 makes a lousy platform for 'proper' guns.

The Germans did a lot of those conversions because they had to. Lack of production capacity+ short development time. No or little MK III/IV production capacity to spare. When you get to the 105 Howitzers (Wespe) the use of too small a chassis starts to show. It carried 32 rounds of ammunition. Four every 4 gun armed vehicles there was a 5th without a gun that acted as an ammo carrier and spare chassis that a gun could be swapped into. The American M7 carried 69 rounds.

Since US produced whooping 25K + of M3 M5 combined, think we can spare some to act as ammo carriers
The M3 starts as 10% wider vehicle, and, earlier, I've suggested lengthening the hull.

If you are talking about a "what if" in which the Americans had some bizarre reason only the M3 light chassis to work with then some of the vehicles make sense. With the M3/M4 chassis and the halftrack chassis available they don't.

US issued many 3in towed AT guns - instead being loathed from GIs, better thing is to mount them to 'my' M3 chassis.
M7 Priest was not ever shipped to the Russians, leaving them with SU-76 to act as indirect mobile fire support. Sending 700 M3/105mm (not only) there makes more sense than another 1000 of light tanks. Ditto for M3/3in.
Sure enough, acquiring of another, say, 3000 of SP artillery 'stead of towed pieces makes Allied forces more mobile, faster to deploy/fire/redeploy, cuts on manpower...

 

[tomo pauk]

My proposal:
-hull elongated between main wheels
-engine in center, simple gearbox couples engine with transmission 'stead of prop shaft
-muffler on lower hull, exhaust under returning part of tracks
-hull extended back, vertical rear

Now that is some 'geschützwagen' - note the much bigger combat compartment, unobstructed by prop shaft, compared with turretless M3 hull (1st pic).

 

[tomo pauk]

The M5 offers itself for a neat conversion.
Deleting of a turret one of engines cuts weight to, perhaps, 12 tons. That leaves us with 148HP, power-to-weight ratio 12,3 HP/ton - almost equal to M4s with Chrysler, or GM engines. That would be the APC; even with no mid-hull stretching the number of troops carried can be as previous M3 conversion, because the engine can go in place previously occupied by radio-man.

The fully-fledged, stretched variant mounts both engines mid-hull. Usable as platform for 3in, 105mm, or better armored APC.

The red boxes depict the new location of engine transmission, blue depicts place for infantry.

 

[parsifal]

im not convinced that light tanks are a waste, mostly because the concept continued after the war. but i would concede its changed considerably since the war. The one that comes to mind are the m-41 Bulldogs and AMX-13s at the heavy end of the spectrum. at the light end you have the LAV-25, and the russian BTR90 and the various turretted versions of the m-113 such as the ARVN ACAV and the australian turetted variant of this concept . The brits developed the scorpian striker and spartans, along with a wide range of other light tanks.

often the line between AC and Light tank is blurred with these vehicles, and a particular role is not envisaged for the type as a whole. they fulfil a wide range of functions, including amphibious tanks, Light and heavy recon, Infantry support, policing, AT and a whole range of other specialised functions.

If you want to draw some arbitrary distinction by calling a light tank a tracked vehicle, and a wheeled vehicle an armoured car, the only difference that might arise from that distinction is that tracked vehicles have traditionally been seen as somewhat more mobile under certain conditions, and can generally deliver more firepower. This however seems a largely academic or theoretical distinction as wheeled vehicles can in fact be faster and still fairly mobile ove rough terrain, and can be fitted with quite heavy armament.

if you wanted to restrict the functions of light tanks in the WWII context to recon (which is not the only function, but we are going to go nuts otherwise), then there is this constant battle between survivability and expendability. You dont want your recons destroyed by Infantry weilding AT rifles, by the same token you dont want to spend so much of your military capital making your Recon vehicles invulnerable, but at excessive cost.

I think like everything it has to be a combination of the two ....having some firepower to deal with some threats, but also enough mobility to out of trouble if need be, and to be done at a cost that is not prohibitive.

Light tanks are also useful in certain specialised roles, like armoured suport in the jungle, amphibious tanks, or in exceptionally rough terrain. As a dangerous generalization Light tanks tend to be less maintenance hungrary than regulsr tanks, because they put less strain on their drive systems

 

[tomo pauk]

On a related issue, too bad the 105 M3 was not tried at US halftracks. While offering a much heavier punch than 75mm, it was substantially less powerful (lower MV) than the M2, so the recoil wouldn't be such an issue?
Or just bolt the muzzle brake on M2, for same (better?) effect.

And, how about this combo: Vickers light tank Mk. VI + 18pdr, later + 25pdr. Another reliable vehicle married with reliable gun.
Before you start laughing, Germans were using those hulls as platforms for 10,5cm M.1916 howitzers, and were satisfied according to Jentz.

 

[Shortround6]

im not convinced that light tanks are a waste, mostly because the concept continued after the war. but i would concede its changed considerably since the war. The one that comes to mind are the m-41 Bulldogs and AMX-13s at the heavy end of the spectrum. at the light end you have the LAV-25, and the russian BTR90 and the various turretted versions of the m-113 such as the ARVN ACAV and the australian turetted variant of this concept . The brits developed the scorpian striker and spartans, along with a wide range of other light tanks.

We may get mired in semantics here, between wheeled tanks (original name for the British Diamler?), tracked armored cars and stretched mission requirements. M-41 bulldog use late/post war technology to pack the firepower of a 76mm Sherman into a very fast chassis, weight of 23.5 tons kind of puts it in the MK IV medium class but with less protection in places. AMX-13 was an air transportable (barely)tank destroyer. It had some rather strange limits as a "tank".

you have left out the most famous fiasco, the M-551 Sheridan. The original "it sings, it dances, it tells jokes, it even washes your dishes and does windows" tank.

The more successful tanks, light and other wise, usually had a clearly defined mission requirement and a reasonable performance requirement. The broader the area that was tried to be covered and the more extreme the requirements the less likely the design was to succeed.

There were (are) two different schools of thought on recon vehicles, one is to try to gather information by stealth and/or bypassing strong points. The other is to "fight" for information, recon troops should be able to blast their way through all but the most determined/well equipped opposition.
Obviously the school in power at a given time influenced a nations purchase of vehicles and the standards for stealth and fighting power changed over time.

WW II and the 50s also brought in the air deliverable and air transportable light tank. A new requirement not exactly inline with the old light tank requirements but overlapping in many ways.

In the early part of WW II light tanks filled out numbers (sometimes at great cost to the crews, British, Italian, Russian and even German MK I and MK II crews), performed recon duties or provided armored support against even less well equipped opponents.
Japanese light tanks worked perfectly well against the Chinese, They were total death traps against US M-3 light tanks which in turn were death traps against German 20-25 ton tanks with High velocity guns.

Light tanks had a place and they still have a place, as long as that place is recognized and it's limits are recognized.
Sticking a wacking big gun on a light vehicle turns it into a self-propelled gun, that is a gun than can propel itself from one firing site to another. It does not always mean that it has turned into a tank destroyer or assault gun let alone a "tank". And unless you have the communications network, the maps and survey crews, and the needed logistics and supply self-propelled guns might not actually be self-propelled artillery.

 

[Shortround6]

On a related issue, too bad the 105 M3 was not tried at US halftracks. While offering a much heavier punch than 75mm, it was substantially less powerful (lower MV) than the M2, so the recoil wouldn't be such an issue?
Or just bolt the muzzle brake on M2, for same (better?) effect.

From wiki "The production started in February 1943 and continued until May 1944; an additional bunch was produced in April-June 1945"

By the time they actually had M-3 howitzers they had M7 self propelled howitzers. And the half track 75mm howitzers were fading from service.

And, how about this combo: Vickers light tank Mk. VI + 18pdr, later + 25pdr. Another reliable vehicle married with reliable gun.
Before you start laughing, Germans were using those hulls as platforms for 10,5cm M.1916 howitzers, and were satisfied according to Jentz.

18pdr was on the way out in the mid 30s.
Germans were satisfied with what? mobility in comparison to 4-6 half starved horses?

A top heavy vehicle with limited ammo capacity, limited gun crew with limited space to work leading to a low rate of fire and, unless a fair amount of work was done, rather limited traverse of the gun 4 degrees total or 4 degrees each side of the center line? A Wespe had 34 degrees of traverse and an M7 had 45 degrees (more to the right than to the left but still?
4 degrees is roughly a width of 667 yds at 10,000yds. If the target is outside of that "pie slice" the vehicle has to be shifted to bring the target into the covered arc rather than just traversing the gun.

 

[tomo pauk]

From wiki "The production started in February 1943 and continued until May 1944; an additional bunch was produced in April-June 1945"

No probs; M3 makes a fine weapon for half track, but more potent, more prolific M2 is available earlier, making it better choice for 13-ton chassis.

By the time they actually had M-3 howitzers they had M7 self propelled howitzers.

The catch is the word 'had'.
Only US forces in MTO were equipped with M7 in some numbers by mid 1943. Their theater 'neighbors' have received only a trickle of M7s (requesting a whooping 5500) and are reliant to towed artillery and small number of barely-adequate Bishops - not very good for an advancing army.
In Asia/Pacific M7 was 1st used in Feb, 1944 (Kwayalein campaign, or even as late as Okinawa campaign, as Osprey's Battle Orders 8 US Marine Corps Pacific Theater of Operations 1944-45 states), so Allied forces need to use towed guns there for most of the time. Think we can consider numbers of M7 deployed in Asia/Pacific as pretty low.
Then we add needs of Red army, US industry was catering for.

And the half track 75mm howitzers were fading from service.

Yep, some were presented as gift to Brits? 75mm was regarded as gun of insufficient power (for artillery branch of Army) much before WW2, hence new 105mm howitzers in Germany, France, US, and 25pdr for UK in 1930s.

18pdr was on the way out in the mid 30s.
Germans were satisfied with what? mobility in comparison to 4-6 half starved horses?
A top heavy vehicle with limited ammo capacity, limited gun crew with limited space to work leading to a low rate of fire and, unless a fair amount of work was done, rather limited traverse of the gun 4 degrees total or 4 degrees each side of the center line? A Wespe had 34 degrees of traverse and an M7 had 45 degrees (more to the right than to the left but still?
4 degrees is roughly a width of 667 yds at 10,000yds. If the target is outside of that "pie slice" the vehicle has to be shifted to bring the target into the covered arc rather than just traversing the gun.

Vickers Mk.VI with 18pdr was feasible in 1930s, a sight unheard of for the time. Cheap reliable, to serve as mobile fire support for other Mk.VIs (even if not upgraded with 25pdr for 1940). Or we can wait for late 1942, for stellar Bishop to arrive, or that Americans give us 75mm on halftracks.
Jokes aside, Brits could've pulled something better. For example, to mount the 25pdr at 'my' M3/M5 hull. Vickers with 10,5cm was just an example; I agree that it was far from ideal combo.

 

[Shortround6]

Perhaps I wasn't clear. that quote is for the production of the M3 105 howitzer. By the time you have any numbers (more than a couple dozen) and can actually move them from the factory to a combat front it is mid 1943. With the Sexton already in progress (prototype completed in June 1942) perhaps we should take another look at the real history:
British did request 5500 M7s, but when?
90 are Shipped to the British in time to be used at El alimein. A little early for the M3 howtizer without a time machine no matter what chassis it is on. British are so short of SP guns that by Oct of 1944 they start converting 102 M7s to Kangaroo APCs.
British had supply problems with M7s because the 105 howitzer was not a standard British round. Solution is to give them more tubes that use non-standard ammo?

Same consideration goes for giving any of these things to the Russians. They never got ANY 105 howitzers so a special supply line would have to be set up. And special is the right word. A single 105 howitzer barrel was good for at least 5000 rounds before it needed replacement. That is about 82.5 tons of projectiles not including cartridge cases or propellant.
SP howitzers were needed on pacific atolls why? It must have been a real problem moving those towed guns 5 miles or less.
You brought up Kwajalein, what did SP guns really bring to the battle?
File:Kwajalein Atoll;p12(map).gif - Wikipedia, the free encyclopedia

The Russians weren't particularly interested in American/British field artillery. I don't know why SP versions would have been greeted with great joy.
To make really good use of SP guns instead of just having a tracked gun you need the command and control to go with it. A better radio net (field phones can't keep up with gun movement) good maps and good survey teams. If the new target is really 5 miles away instead of 4 1/2 your first ranging shot may just land on your own forward observer.

A self propelled 18pdr wasn't a new idea in 1935.

Birch gun - Wikipedia, the free encyclopedia

The British knew what they wanted and MK VI chassis wasn't it.

BTW, I am not sure the British ever got ANY 75mm howitzers on half tracks, they did get 75mm guns on half tracks.

 

[tomo pauk]

Perhaps I wasn't clear. that quote is for the production of the M3 105 howitzer. By the time you have any numbers (more than a couple dozen) and can actually move them from the factory to a combat front it is mid 1943.

But, I DON't advocate M3 as a weapon for 'my' M3/M5 (light tank, not half track) chassis - it's always M2

With the Sexton already in progress (prototype completed in June 1942) perhaps we should take another look at the real history:

As we know, prototypes don't equate combat usage

British did request 5500 M7s, but when?

Perhaps someone can enlighten us on this; my take is mid 1942?

90 are Shipped to the British in time to be used at El alimein. A little early for the M3 howtizer without a time machine no matter what chassis it is on.

I've stated earlier that time of use should have been summer of 1943.

British are so short of SP guns that by Oct of 1944 they start converting 102 M7s to Kangaroo APCs.
British had supply problems with M7s because the 105 howitzer was not a standard British round. Solution is to give them more tubes that use non-standard ammo?

By late 1944 Brits have Sextons in good number, while they don't have any APCs (not unless we supply them with M3/M5 APCs ). So they create Cangaroos.
As for supply problems, we know that they used 2 x foreign 0,3xy cal ammo types, US .50in, US 75mm. I'd say having artillery units with cross-country capability while requiring less man to operate out weights adding another ammo type. Plus, to quote myself from 2 posts before:

Jokes aside, Brits could've pulled something better. For example, to mount the 25pdr at 'my' M3/M5 hull.

Same consideration goes for giving any of these things to the Russians. They never got ANY 105 howitzers so a special supply line would have to be set up. And special is the right word. A single 105 howitzer barrel was good for at least 5000 rounds before it needed replacement. That is about 82.5 tons of projectiles not including cartridge cases or propellant.

Same thing for Russians. They used 8 (eight, at least) Western ammo types, so why would the addition of make things such a problem? BTW, just a right place for 3in ATG on 'my' hull.

SP howitzers were needed on pacific atolls why? It must have been a real problem moving those towed guns 5 miles or less.
You brought up Kwajalein, what did SP guns really bring to the battle?
File:Kwajalein Atoll;p12(map).gif - Wikipedia, the free encyclopedia

SP howitzers have same role as ordinary artillery. So the need was there, in all Asia/Pacific war theater. Alas, there was almost no SP howitzers there.
I've brought Kwajalein operation in order to find out when and where M7 have had their combat debut on that half of Earth.

The Russians weren't particularly interested in American/British field artillery. I don't know why SP versions would have been greeted with great joy.

Russians never employed any Western SP artillery.
Decent SP in 105mm calibre is way better than any 3in class gun for indirect direct (excluding AT role, but we ship them 3in on M3 for those tasks) fire support, and if any Army favored heavier shell over MV, that was Red Army.

To make really good use of SP guns instead of just having a tracked gun you need the command and control to go with it. A better radio net (field phones can't keep up with gun movement) good maps and good survey teams. If the new target is really 5 miles away instead of 4 1/2 your first ranging shot may just land on your own forward observer.

We won't strip the radios from our vehicles

A self propelled 18pdr wasn't a new idea in 1935.

Birch gun - Wikipedia, the free encyclopedia

Indeed, Birch gun was good idea...

The British knew what they wanted and MK VI chassis wasn't it.

...but not ideal. For 100 Birch guns one could've purchased 200 Mk.VIs with 18/25pdr, deal with vehicle that is in production by 1940 (far younger than the Vicker Medium), having no problems to divert 50 pcs to Malaya, leaving a more generous chassis for tank production (if we want the Medium still).
Ceterum censeo, I don't Mk.VI as hull for SP howitzer to be the best choice. Simply the one that is available feasible in 'dark years'.

BTW, I am not sure the British ever got ANY 75mm howitzers on half tracks, they did get 75mm guns on half tracks.

Of course, it's gun I've meant, not howitzers

 

[tomo pauk]

Let's put some steel on our steel; the superstructure of Wespe serves well for demonstration purposes. Note the roomier fighting compartment, pushing height to be on par with M7 priest, but perhaps allowing for greater ammo load