WI Allies adopt concept of Assault gun in WW2

Redbeard

Banned
With the abundance of wallied turreted tanks specialised for infantry support there really wasn't a vacant slot for the assault gun, but I'd still say that the assault gun was more than a "poor man's tank", it had a number of distinct advantages over the turreted tanks, and of course some disadvantages too.

The assault gun first of all could offer a very low silhuette, and for the same total vehicle weight also better protection and a bigger gun - at a lower cost. That is not bad at all, and I'll have to add one more advantage - it made it possible to utilise basic vehicle designs and their production lines that otherwise had become obsolescent.

The absense of a turret of course also meant some obvious tactical disadvantages and meant that assault guns was even more dependent of infantry support than tanks. But as also tanks by WWII were very dependent on infantry support I think the margin was very narrow.

The original role of the assault gun was offensive, as the name also clearly states, and the "tragic" is, that by the time assault guns were present in numbers and optimised design (like the Pz IV Brummbär) the Wehrmacht had very few offensive tasks. This meant the original assault guns (StuG IIIs manned by artillery) very soon transforming into very effective TD units and the assault gun design being developed into specialised TD designs (Jpz IV and Jagdpanther). For a TD unit I would anytime prefer a Jpz IV over an M10 or a JagdPanther over an M36.

But if they were so good why didn't the wallies need them then? Well, mainly because what the wallies had was good enough for the job and available in abundant numbers - so why bother? Better use the effort on good food and clean underwear - that is something the soldiers will understand and appreciate.
 
A Churchill chassis would be overkill.

Didn't stop the designers from giving it a try. The results were... poor.

infantry-mk-iv-churchill-mk-i-3-inch-gun-carrier-011.jpg
 

Redbeard

Banned
That would be a "Maus Trap"
A 203mm howitzer on a Sherman chassis would have been very useful on Iwo Jima or Okinawa.

Now we're at this subject I have a general question.

We usually refer to assault guns and infantry support tanks as "bunker busters" and in early WWII that usually meant at least a 75 mm gun or howitzer and later 105-152mm. Against buildings or a field fortification of soil and timber I can clearly imagine how a direct fire HE shell will work, but how was the intended tactic against concrete pill boxes like seen in many defensive lines in WWII? Even 152mm or 203 mm HE shells will do very little damage on a concrete structure. I have actually as part of my training (many years ago) been placed inside a concrete bunker on top of which was detonated a large number of 155 mm shells. It was quite noisy and dusty and a bit shaky, but the concrete was hardly scratched.

So I suppose they didn't intend to just fire HE shells at the concrete and AP shells from a howitzer or even from an AT gun wouldn't make that much of an impression on 1+ meter of reinforced concrete. But what then? Was the intention to fire at the "slots" in the bunker to suppress fire from the bunker and then bring up demolition teams or flame throwers?
 
If at first you don't succeed, use a bigger hammer!
Churchill_AVRE_of_617th_Assault_Squadron%2C_Royal_Engineers_near_Geilenkirchen%2C_Germany%2C_19_November_1944._B11963.jpg

It's an 11" spigot mortar firing a 40lb bomb (28lb charge inside, I think it was mostly firing HESH).
 
IMHO - it's a wonder that Britain didn't go down that route - pre-war - as an addition to turreted tanks. Why, two reasons, money - would be cheaper and quicker to build, and with no turret, they can have an AFV with a bigger armament, without any problems on the railways.
 

Deleted member 1487

That would be a "Maus Trap"
A 203mm howitzer on a Sherman chassis would have been very useful on Iwo Jima or Okinawa.
https://en.wikipedia.org/wiki/T92_Howitzer_Motor_Carriage
HMC_T92.png



Now we're at this subject I have a general question.

We usually refer to assault guns and infantry support tanks as "bunker busters" and in early WWII that usually meant at least a 75 mm gun or howitzer and later 105-152mm. Against buildings or a field fortification of soil and timber I can clearly imagine how a direct fire HE shell will work, but how was the intended tactic against concrete pill boxes like seen in many defensive lines in WWII? Even 152mm or 203 mm HE shells will do very little damage on a concrete structure. I have actually as part of my training (many years ago) been placed inside a concrete bunker on top of which was detonated a large number of 155 mm shells. It was quite noisy and dusty and a bit shaky, but the concrete was hardly scratched.

So I suppose they didn't intend to just fire HE shells at the concrete and AP shells from a howitzer or even from an AT gun wouldn't make that much of an impression on 1+ meter of reinforced concrete. But what then? Was the intention to fire at the "slots" in the bunker to suppress fire from the bunker and then bring up demolition teams or flame throwers?
The structure, but the shockwave of the big blast would cause some problems for the guys inside. Enough of that, whether 1 or 100, would concuss or kill.
Then there was the British HESH round:
https://en.wikipedia.org/wiki/High-explosive_squash_head
HESH was developed by Charles Dennistoun Burney in the 1940s for the British war effort, originally as an anti-fortification "wallbuster" munition for use against concrete. He also led British developments in recoilless rifles as a means to deliver the shell. An early application of the HESH principle was the Royal Engineers AVRE's 165mm demolition gun.

HESH rounds are thin metal shells filled with plastic explosive and a delayed-action base fuze. The plastic explosive is "squashed" against the surface of the target on impact and spreads out to form a disc or "pat" of explosive. The base fuze detonates the explosive milliseconds later, creating a shock wave that, owing to its large surface area and direct contact with the target, is transmitted through the material. In the case of the metal armour of a tank, the compression shock wave is conducted through the armour to the point where it reaches the metal/air interface (the hollow crew compartment), where some of the energy is reflected as a tension wave. At the point where the compression and tension waves intersect, a high-stress zone is created in the metal, causing pieces of steel to be projected off the interior wall at high velocity. This fragmentation by blast wave is known as spalling, with the fragments themselves known as spall. The spall travels through the interior of the vehicle at high velocity, killing or injuring the crew, damaging equipment, and/or igniting ammunition and fuel. Unlike high-explosive anti-tank (HEAT) rounds, which are shaped charge ammunition, HESH shells are not specifically designed to perforate the armour of main battle tanks. HESH shells rely instead on the transmission of the shock wave through the solid steel armour.

HESH ammunition has good general purpose use, being effective against most targets, though the round is generally used at relatively low velocities because high velocity excessively disperses the pat of explosive. While only effective against tanks without spaced armour or spall liners, the round is still highly favoured for combat demolition purposes. The flattened high-velocity explosive pat is capable of destroying concrete constructions much faster than a HEAT round (which is designed for armour penetration), and without the dangerous fragmentation of a traditional high-explosive (HE) fragmentation round.
https://en.wikipedia.org/wiki/Royal_Ordnance_L9
 
The US 90mm firing AP was good enough to penetrate concrete bunkers, 4-6 rounds in the same location could break through 6' of concrete, followed by some HE to finish the job.
 
Quarter inch welded rebar.

Enough steel to reinforce 20cm thick concrete to resist the energy of a 9 cm AP round would turn it into more steel armor than concrete. Concretes strength is in resisting compression, hammers & AP rounds create tension loads. Making the concrete massively thicker enables resistance to tension loads.
 
I believe the M40 (155mm GMC) was used successfully to bust concrete bunkers during the Siegfried line campaign. Close range using its higher muzzle velocity relative to a howitzer.
 
What about the various CS models of British tanks - if only they had adequate HE shell ammunition? The Matilda CS (often called the Matilda II) was very popular with the Australians. The Churchill 1 had a gun in the glacis plate. You also have Sexton, Priest, and various half-track (the first American tank destroyer) or wheeled vehicles (the French had a very nice armoured AT gun mounted on a lorry chassis). OK they are all tanks or SP guns.
 
The US 90mm firing AP was good enough to penetrate concrete bunkers, 4-6 rounds in the same location could break through 6' of concrete, followed by some HE to finish the job.
I've seen reference to "Pick and Shovel" firing, where the tank gunner alternates AP and HE rounds without changing the aiming point, until the desired result...used in Korea against caves and pillboxes.
 
Take a look at the diagrams of the concrete emplacements on the Normandy coast & note the thickness. One or two hits from a naval 10 - 13 cm AP round was often enough for the MG & AT gun bunkers. The trick was getting a direct hit on the concrete face.
 
I wonder what the heaviest gun that could have been squeezed into a Lee/Grant sponson .

17 pounder is out of question I'm assuming
 
I wonder what the heaviest gun that could have been squeezed into a Lee/Grant sponson .

17 pounder is out of question I'm assuming

Not sure the sponson is the area of initial interest for a Grant assault gun. The turret has a ring dia of 54.5 inches, meaning a different turret with 3 man crew and a 75mm M2/M3/NA75 or perhaps a 57mm/6pdr could be fitted. Then, you could move to the sponson,, and do all sorts of weird and wonderful things. Maybe put a 3.7 howitzer there, 105mm perhaps. Try a 20mm Oerlikon and a flamegun in a sort of hi-lo coax mount. Always thought a Lee/Grant assault vehicle was a great idea but for the M-7 HMC, which sort of took precedence. You produce a tank with a standard turret toting a GP 75mm, in addition to some close range mayhem from the sponson.
 
How the 95mm howitzer that was used on the Churchill for the main turret.
IIRC, one of the two, 3.7 or 95, fits in the same gun slide as the 6 pdr and the NA75, so, guaranteed fit and fewer probs for your ordnance guys.
Says edit, but it's more of a postscript; such a vehicle as imagined here might be too obvious a target in Europe, but considering the M-3 towering height was occasionally considered a plus in the CBI, a small number might be really useful there.
 
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