Shipbucket

The case of AT guns versus armour in tanks is the same to asking what came first, the egg or chicken?
At the beginning of WW2 the standard AT gun was a 2pdr (40mm) for the British guns, and 37mm for most other European countries. By 1941 the usual AT gun was a 6pdr (57mm) for British guns the German usually had the 50mm gun while not uncommon were 47mm guns.
Also worth noting is the fact that at the start of WW2 infantry units had a At rifle, usually a 0.5" gun (like Britain's Boise) and Russia had a 14.5 mm gun (PTRD). By 1942 most countries were developing other AT weapons (Britain had the PIAT, while other countries were usually developing rocket propelled weapons, the US Bazooka or German Panzerfaust, being a case in point).

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"Never fear to try on something new. Remember that the Titanic was built by professionals, and the Ark by an amateur"

Hmm. Unless you carry the gun armor race back to crossbow/armored knight, the tank (chicken) came first before the AT gun. (egg).

To be more precise, there is not such thing like AT gun. Most of guns can be use in AT role it's only a case of ammo.

Pretty common for US the AT gun was just the Canon de 75 modèle 1897... it became "AT" when someone design a special ammo for that role, before that it was just an field artillery piece.

So what was first Tank or AT gun? The answer is simple... a gun.

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Nobody expects the Imperial Inquisition!

Hmm.

US antitank guns follow a peculiar line of development. In WW 1, for them, there was no need for an antitank gun per se, so none was US developed or fielded as the Germans did with their 7.5 cm and 10.5 cm howitzers.

In the interwar years the US developed a heavy 12.7 mm machine gun, the Browning .50 (half inch) from the Browning 7.62 mm gun (.30 or 3/10ths inch) as an anti-material weapon for use against both vehicles and planes. It was the nearest thing to an anti-tank gun the US had before 1935.

When it came time to develop a dedicated anti-tank gun, the Canon de 75 Mlle 97 was not the American gun of choice. The first gun chosen was an old Driggs Schroeder naval design that very closely resembled the Pak 36 antitank guns the Americans "acquired" from the Germans.

This model, the M-3, entered US service very late (1940-1941), and formed the anti-tank basis for both towed and vehicle mounted antitank weapons in US Army service.

When it came time to field a medium infantry support tank (char d'assault), to work with the infantry (the US Army was heavily influenced by French Army doctrine and technology) the gun chosen was to be an anti-material, anti-infantry dual purpose weapon of sufficient accuracy, lightness and rapidity of fire to emulate the Char B-1's clumsy dual purpose gun armament in the assault role. The Canon de 75 Mlle 97 (a gun/howitzer) was the compromise weapon for the assault tank. This showed up on the M-2/M-3 tank in the same exact configuration as the 75 mm ABS SA 35 howitzer served in the Char B-1.

The American licensed canon de 75 French weapon was available American gun makers could make and did make it as the most expedient off the shelf weapon to match the urgent US Army requirement for a gun motor carriage howitzer. This was not intended as an antitank weapon at all. It lacked the optimum muzzle velocity (800 m/s) and ammunition desired. The ammunition had to be back designed to the gun. Never a desirable technical solution.

The US Army had its 37 mm Driggs Schroeder derived naval gun as the M-3 which was fielded in the Stuart tank, as towed antitank guns and on the back of various trucks and half tracks in their first generation destroyers. This served well despite the surprise encounters with the better than expected PZ III and PZ IV tanks in North Africa.

The next antitank gun the Americans used, again was derived from a naval gun. It was more or less an American copy of the British 6 pounder anti-tank gun. The British gun, the OQF 6 pounder was a modernized Hotchkiss as designed by Woolwich Arsenal. The American M-1 version was almost a direct monkey copy with a more simplified breech block and again back designed high explosive and armor piercing shell to meet American manufacturing methods, technology, and US Army doctrine, which was more French than British when it came to artillery.

The first true American designed (not copied) antitank gun was based in the US 3 inch naval gun designed in 1890. This was the US Army's heavy and clumsy M-5. The US army mated the WWI abortion derived from it , its antiaircraft gun, the 3 inch M-1918, to a modern 105mm M-2/M-3 towed howitzer carriage and recuperator mount and called that an anti-tank gun. Even at that, the gun had to be derated with a reduced volume breech chamber and a shorter barrel so its weight and recoil forces would fit within the limits of a towed howitzer mount and use single piece ammunition. Bass Ackwards design in the gun And once again the gun came first and the ammunition had to be back designed to fit it. These guns had breech accidents as a result of the clumsy design path.

The other 3 inch guns were the M-1 and the M-7. Here it gets even more confusing. The M-7 was another design based on the 1918, but this monster was a full direct copy of the anti-aircraft gun with a simplified modernized breech. This was shoved into the M-6 heavy tank and like the naval gun from which it originally came, it used two piece shell/charge feed. The gun was only one of many engineering disasters in that tank. It was a clumsy slow loading weapon. It showed up eventually in the M-10 tank destroyer where the open fighting compartment and much revised handling arrangements enabled the gun to be adequately served, even with the two piece ammunition. Oddly enough this gun carriage tank destroyer weapon was used more as a counterbattery field artillery support weapon than as an anti-tank gun. Yet again the gun came first, and then the ammunition. But at least the breech failures were abeyed.

The M-1 76 mm (3 inch) gun that wound up in the Sherman tank was yet again a rework of the M-5 (see above) with more breech chamber redesigns, more new ammunition developed and different trunnion arrangements to fit into a turret originally designed for the follow on to the Sherman tank (the T-20XX series, which evolved into the M-26). The T-20-25 engineering failed in everything except the turret which finally came with the first specialized antitank gun fitted to a proposed American medium tank. That turret would fit a Sherman turret ring, and so it was slapped onto any Sherman hull and sent just in time to fight post Normandy (France August 1944).

The last of the fielded WW II anti-tank guns the Americans used, was the 90 mm M1/2/3 series of anti-aircraft guns. Once again, the ammunition for the artillery support and anti-tank roles came after the gun was redesigned to be plonked into tank destroyers and tanks. Since that ammunition also worked in the anti-aircraft gun, this sort of made the 90 mm the American version of the 88. This sort of fits with:


but it is not the way things are supposed to work. You design the shell and charge first (German or French method) to the intended purpose and then wrap the gun around that. The Americans tended to do things backwards and/or sideways. They designed ammunition and then a naval gun or an anti-aircraft gun (a direct fire rifle with reasonable muzzle velocity to reach high altitudes or punch holes in ships) and then when they ran into a tank they could not defeat, they adapted the existent gun (usually reduced capacity) to fit whatever carriage they could put under it. And then they would design new ammunition back to the reduced gun to fit the bodged result.

It worked, but it could hardly be called efficient use of resources and time. And the results were often not what was expected or intended.

Sometimes the back method is the best one. 8,8 cm Flak 18 (and next models) was NOT design as AT piece, it was an AA gun. Also Soviet divisional guns that ware used as AT piece, howitzers and heavy howitzers again used in AT role. Italian Cannone da 90/53... ect.

Sometimes the gun first - ammo later approach was successful in both terms of capability and economic.

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Nobody expects the Imperial Inquisition!

The Italian artillery piece was at least designed as a counterbattery rifle and was provided effecto pronto ammunition as well as AP shot. The German 88 (3.5 inch) was discovered by battlefield accident. (a clumsy one that Germans exploited.) was because the gun shot to pieces the British and French tanks with its current high explosive ammunition (1940-1942) as a desperate expedient when the Pak 36 failed in France. When the better Allied tanks showed up (Shermans and T-34s) the Germans went ahead and developed ammunition and then HV 75 mm guns to deal with it in that short order. The British developed a new 3 inch gun (called a 77 mm) to deal with the PZ IV and the expected follow on in their turn. A new gun that was too.

The US 90 mm was proposed as an antitank gun as early as 1941 when the German 88 accident became well known. Righto, shove the gun into a tank or tank destroyer and away the US Army would go.

The problem is that it takes time to design a proper armor piercing shell to fit the gun. Much more time than it would be to design the armor piercing shell and charge and then design the gun around it, (British 17 pounder was so designed as an in war project.). The US 90 mm existed and was undergoing proof as an AAA gun when the proposal was made.

The Americans took that gun and did to it exactly what they did to their 3 inch antiaircraft gun. They reduced its breech volume, changed the breech block, lightened and shortened the barrel to fit it on an M-3 type motor carriage, and then they had to design the ammunition for the modified gun. The Germans simply built a big tank and shoved an 88 into it.

Admittedly they did this very quickly (about a year and a half for the modified guns and prototype ammunition.) But there is a problem. Guns, even proven designs, have to be range fired to establish ballistics for the ammunition. And if the ammunition is different in mass and charge, then the firing tables could take up to two years to compile.

Now that is not late 20th century tech. This firing table compilation was done by 1930s pencil and paper and analog computer, most of it was already worked out for FLAK between 1937-1940 and yet the 90 mm gun was still not ready in the original AAA tables before Pearl Harbor. As a reworked gun, the range tables had to be started from zero again. By tables I mean the tables for high explosive shell for field artillery work, then more tables for AP shot, more tables for the APC shells, more for the American hyper-shot which was their version of British composite rigid shot, and for their shaped charge bunker buster shells.

Everybody had to do this work and it finished out with mixed results. There was a man named Grigory Kulik who oversaw this kind of work for Russian artillery. He was a disaster who crippled the Russian field artillery and anti-tank programs. I seem to remember that what he did to the L-11 and F-34 guns that were fitted to the T-34 tank resulted in engineering disasters that negated early Russian technological tank gun superiority over the Germans. I almost think of him as the far worse Russian version of the American Leslie McNair. The Russian field guns (their artillery park) which were finally supplied with dual purpose sets of ammunition (1943) did not happen until Kulik was court martialed and cashiered in 1942. American problems with their own artillery persisted into 1944 until McNair was blown up by the American army air force. Then they managed to start sorting themselves out (If you think the L-11 and F-34 gun controversy had to wait for Ustinov to sort it out, the eerily similar US 75 mm Sherman 76 mm Sherman gun debacle had to wait for the Normandy tank massacre, and McNair bombed outside St Lo to clear the political way for the Americans' Army Ordnance.

McNair's removal also cleared the way for the American 90 mm tank destroyer. (M-36 Jackson) It arrived just barely in time for the 2nd Battle of Ardennes. (Battle of the Bulge-arguably the American version of Kursk on a smaller scale.) And I do see it is historically eerie a small example in how the Americans were sorting themselves out in material the same way the Russians did at Kursk.

So it did not quite work out (for the Americans). It took a lot of time to fix these mistakes and delayed programs, and bring the modified material to acceptable readiness. You could argue that the Americans never quite caught up to either the British or the Russians with their own material until after the war was 90% won.