The 57mm / 6 pdr antitank gun modified

What if the US Army and British Army had started modifying the 57mm M1 and 6 pdr antitank guns like the British did to the 6 pdr tank mounted gun? That is, they bore the gun out to 75mm and make it capable of taking 75mm M3 ammunition.

Now, this would have reduced the antitank capacity of the gun slightly but it would have greatly increased its value as an HE support fire weapon for infantry units.

The versions with shoulder laying would have had to have the US hand wheel laying traverse and elevation added to them as the tank gun did. It should have been possible to issue units new guns bored out and then re-manufacture the guns replaced to the same standard and re-issue them.

 

6pdr 846 m/s

75mm M3 619 m/s

Well lets look at the obvious points.

Positive

Better HE shell


Negative

Less accurate due to more shell drop

Lacks a high velocity shell. The 6pdr APDS shell was capable of penetrating 130mm.

14lb shell vs a 6lb shell. An important factor when manhandling the gun and ammo.

Overview

A 75mm conversion would allow the cannon to be much more effective in defense against infantry and light vehicles.
However the loss of accuracy and APDS would reduce it's ability against attacking tanks.
As the war progressed Allied artillery became more and more dominant reducing the need for a defensive direct fire HE gun.

On the offense I'd say it would have been appreciated by the infantry but I couldn't say it would have been used very often due to the time required to position and set up.

 

You nend up with the performance of a sawn off 75mm gun! If you want to kill tanks the 57mm/.6 Pdr was pretty good for 1942 and get even better in 1944 with APDS. .

There were plenty of light cannons @ 75,mm - the original M1897 French gun was pretty much a classic.

 

You end up with a gun that penetrates about 100 mm of armor instead of 110 to 120mm (depending on what round you're using). Still sufficient for most German AFV. Since virtually any US division in the ETO has a tank destroyer battalion attached it has the means to deal with German armor outside the battalion and regimental AT guns. The same holds true for the British. As it was, at least in the US divisions, the 57mm slowly was abandoned and the crews turned into extra infantry. In armored infantry battalions the guns disappeared pretty quickly after D-Day when it became apparent that they were all but worthless given an armored division's number of AFV with guns to deal with enemy tanks.
So, as antitank guns, the 57mm was pretty much seen as marginal to worthless.
In the MTO (Italy) that was much more obvious. Why haul a gun around that won't face a German tank in the next six months and has little other use?

The US guns are pulled by a 1 1/2 ton truck that carries the ammunition. So, the weight difference isn't a huge issue. The US gun has an 8 man crew, so handling slightly heavier ammunition isn't a major problem in that sense either. At worse you add an additional truck towing an M10 ammunition trailer with additional rounds.
The British haul theirs around with a Lloyd carrier usually so there's somewhat more of an issue there. But, that could be fixed easily enough providing a limber to haul the ready ammo with. Again, the crew is large enough that the ammunition weight difference is irrelevant.


This comes back to the HE shell. That switch suddenly makes the gun very valuable. Now it can bust up buildings being used for direct fire support of the infantry. It can beef up infantry unit's firepower against enemy infantry in the same way. Much like the situation with the 2 pdr early in the war, the lack of an effective HE shell makes the gun far less valuable rather than more valuable because its armor piercing performance is slightly better than the competition.
That's why the 6 pdr tank gun got bored out. As a 75mm it was far more valuable than as a slightly better, single use, antitank gun.

The difference now is that in a US infantry regiment they have 18 still useful AT guns when needed for that purpose and 18 effective HE firing 75mm guns for support the other 90% of the time when they don't need the antitank gun capacity. With the British, the 6 pdr could continue in service in the divisional antitank regiment where it is supposed to be primarily for AT use. The regimental guns could get the conversion making them more valuable to the infantry.

In any case, the Allies don't have the problem the Germans do when it comes to antitank systems in infantry units. If anything, the US and British have a plethora of readily available antitank weapons to deal with German armor. In fact, given the historical record, they have far too many that are too specialized for that purpose and if those weapons aren't capable of being used in other roles they are worthless. The abandoning of 57mm guns in US units is an excellent example of how troops in the field took rational steps to rid themselves of near worthless weapons and turn the remaining assets into something useful... more infantry. If the guns were useful, they'd have remained in service.

 

That's what mortars are for.

 

While anticipating the need for more infantry can't reasonably be expected, it did in fact come to pass. Discarding the 57mm and turning their crews into replacement infantry served a distinct and unavoidable problem. If you make the gun into a more effective weapon, does its effectiveness offset the irreplaceable addition of infantry replacements?

In the long run does American divisions see a net gain or loss, especially in the last year of the war in Europe?

 

It'd be hard to say for sure. In Korea, the US Army's infantry units found the 75mm recoilless rifle invaluable and took the trouble to haul it along even in difficult terrain. By contrast, the 57mm recoilless was considered too small to be as useful. Here you have a WW 2 equivalent with a 75mm towed gun. So, it is possible that it would have been seen as a valuable weapon where the 57mm was not.
In armored infantry units I'd suspect either way the guns would disappear as they were desperately short of infantry all the time and had little need for such weapons given the ready availability of tanks to perform their role.

 

One problem is the idea about "discarding" the 57mm seems entirely generated by the wargaming industry of the 1970s. It has no real basis in fact. The sole evidence for it are the particular circumstances of the U.S. VIII Corps in the Ardennes in December 1944. Its divisions, the 106th, 28th, and 4th utilized various ad hoc measures to adapt to the extended front of the corps, including using elements of the Infantry Regiment Cannon and AT companies as riflemen. There is little evidence it was a universal practice; instead we have numerous accounts of the use of the 57mm - and dissatisfaction with its performance, cuminating in the postwar ETOUSA General Board reports, which recommended its replacement with a tank.

Both the Americans and British believed in a layered AT defense, starting at the battalion and brigade/regiment with the 6-pdr/57mm, augmented by heavier weapons - assigned in the case of the British divisional AT Regiment RA and attached in the case of the U.S. TD Battalion. Neither would have accepted discarding the one to be replaced by the other.

Minor point, the Ordnance Q.F. 75mm was not a "bored-out 6-pdr", which was an impossibility. It was a new barrel and chamber mated to the elevation, traverse, and breech mechanism of the 6-pdr.

 

In any case, the original premise holds: A 75mm version would be more useful than the 6 pdr. and it was possible to do on the same carriage just as it had been done with the tank gun.

 

No need for it. The US Army already had a 75mm field/antitank weapon in its inventory, the M1897 series field gun on the M2 series split trail carriage. The weight was higher than the 6 pdr (3400 lbs) but it could fire the full range of 75mm ammunition. There was also the 75mm howitzer, which was pretty light and handy and could fire HEAT when neccessary. If the US Army had really wanted to give the anti-tank companies of the infantry regiments a little extra HE punch, then they could have swapped out a few 6 pdrs and replaced them at least temporarily with 75mm pieces already in the inventory. I suppose that could have been done if needed, depending on the tactical situation. But why complicate the production lines, repair, training etc with a new type which will be of only limited utility and less effective in the AT role? If I was an infantry regimental commander I would have wanted those 6 pdrs to guard against the panzer danger, diminishing though it was by 1944.

 

I endorse Rich's comments and would like to add that two points

1. Dissatisfaction with the 57mm gun was a US Army phenomena not shared by the British or Red Army. The British Army had a lot of confidence in the 6 Pdr. 6pdrs were the reason the "snipe" position at El Alamein was littered with KO'd tanks. A 6 pdr knocked out the first Tiger engaged in Tunisa. It was preferred by 50 Div in Normandy over the 17 Pdr. The Red Army introduced the T84 SP version of the 57,mm gun in mid 1944, which shows confidence by a country with substantial reserves of other higher calibre equipment. The issue may have been that the 57mm was not sold well internally, leaving soldiers to wonder whether it was good enough give nthat tanks had 75mm guns. One reason for the 50th British Div's confidence may have been the fire power to all 6 Pdr gunners showing how well the APDS round worked.

2. The 21 Army Group OR study on anti tank guns in the Ardennes concluded that SP guns were better on the grounds of survivability. The post war debate about the merits of tanks v anti tank guns was clouded by internal politics of the relevant armies. The US TD branch was no-one's child. The mantra that 'the best anti tank weapon is another tank' was in a lot of service material.

 

APDS was pretty late war itself wasn't it? The 75mm mountain howitzer had a HEAT round that would penetrate ~90mm and 75mm RR HEAT rounds penetrated around 100mm so a larger investment in the 75mm could well end up with a HEAT round with almost the penetration the 6 pdr.

 

No need to do that (a second time). Both had that kind of infantry support gun. It was installed in their tanks. Which was a rather good sollution for it gave the gun far better mobility than a towed gun. Furthermore both armies didn't have a powerful artillery, they had a very powerful artillery.

 

6 Pdr was issued in time for D Day in 1944. The 6 Pdr APBC was good enough to deal with the Mk III and Mk IV and the side armour of the Panther. .

 

The thing is it all becomes a chicken and egg argument. The M2 75mm Field Gun was completed in 1938 after years of development as an improved field gun...just in time for the development of the M2 105mm Howitzer to displace it. However, with a few more modifications, giving the gunner control of both elevation and traverse, it was seen to be an effective heavy AT gun as the M2A2 and A3 75mm Antitank Gun (about 1,000 produced in 1940 and 1941). It was originally intended for the AT Battery to be formed for each FA Battalion, but then got absorbed as the armament for the early "tank hunters" (AKA Tank Destroyers by late 1941). Then, when it was decided to go for a heavier weapon yet the 3" AAA was converted and the M2/M2A2/M2A3 Guns became redundant by late 1942.

There was no reason though to give them to the Infantry instead of the 57mm. It was considered, but the 75mm was simply too heavy...and the high-explosive direct support role was given to the battalion mortars and the Regimental Cannon Company anyway, which in its original iteration was six SP M1897 SP Guns (T12) and two SP M2 105mm Guns (T19). That lasted until mid 1943 when McNair, in an obsessive search for fat to trim, decided the towed M3 105mm Howitzer was the better armament for the Cannon Company (he tended, like most artillerymen, to not like SP mounts and he also wanted the personnel savings). Unfortunately, substituting the towed weapon meant direct fire wasn't really an option, so like the 15cm sIG (we never saw the possibility using the M1 75mm Howitzer like the 7.5cm leIG) it became an indirect fire company dedicated to support of the regiment as a whole.

 

1. The British did share the dissatisfaction with the 6-pdr, just as the Americans did...at the end of the war. And the Americans made good use of them as well, witness the actions at La Abbaye Blanche and St Barthelemy in August, and at Dom Butgenbach in December. The 57mm was an important component of the defense over and over again, but the narrative got taken over by SPI back in the 1980s and certain things became articles of faith...the 57mm was discarded, all American infantry units collected additional BAR, and so on...

BTW, the "Red Army T84" was actually the U.S. Army's T48 SP 57mm Gun, It was used by the Red Army, but it wasn't introduced by them.

2. Yep, the assessment was McNair erred badly. The best Infantry Antitank Gun was either recoil-less or SP. Given the problems found with the TD gun carriages it was also realized the best SP AT weapon was a tank. It also made the best direct fire support weapon, which meant the final organization of the Infantry used tanks as a combined AT/HE support weapon augmented by a heavy mortar company.

 

I simply don't see the need for an extra piece of equipment when you already have items in the inventory in quantity that can fill the same roles adequately enough. The 57 wasn't ideal, but with the right ammo it could and did kill even heavy German tanks. The existing 75 pieces were not ideal, but they were THERE and they could have been used if the tactical need had been considered critical enough. Okay, the M3 how was not ideal either, but it was there too if an RCT really needed close HE support. Yes, perhaps RCL and/or SPs were the ultimate answer, but why screw up your production line when there is no urgent need to do so? The RCL was due to appear in 1945, it was under development and lines for it were being set up. Assuming that everybody had agreed on the neccessity for this bastard 75 AT piece, how long would it have taken to get such a redundant weapon into service? Diverting design effort and factory space to another weapon that would have quickly become obsolescent anyway makes no sense, especially when you have something even better close to coming into service. During a major war, armies and ordnance establishments have limited time and urgent needs and they can't fiddle about with types that duplicate the functions of existing weapons.