Col Judge (210cav) here's your topic! I assume you have first hand experience!
Just to kick off, in the previous Monty topic, there was a lot of discussion about anti-tank rifles, particularly the Boyes.
It's important to remember, that in 1939 when the war began, most armies had somewhat similar equipment. Armour on tanks was much thinner than it would later become, and anti-tank rifles could, in the right hands be extremely potent. The Boyes had a .55" cartridge, about 13-15mm (the Bofors anti - tank gun was only 25mm). It had a kick like a mule when fired.
Like wise, the anti-tank guns were in many cases compatible. The performance of the German 37mm Pak 35/36 was not worse than those of other countries. The greatest drawback of the British 2pdr was it's inability to fire a high explosive shell, but this was mitigated in British armoured units by having one tank in each troop armed with a 3" (?) howitzer. Most countries A/T guns were around 30mm calibre.
As regards German use of the 88mm Flak gun in the A/T role, a next door neighbour of ours, who commanded a battery of 3.7" anti-aircraft guns in the desert, told me that this (British) gun had a performance at least the equal of the "88", but they were expressly forbidden to employ them as A/T guns as it strained the carriage too much! This is never mentioned when "88"s are discussed. Presumably the American 90mm was also similarly derived from an anti-aircraft gun.
The German were inveterate tinkerers with artillery generally during the war. Rather than settle on a few solid pieces and churn them out, they preferred to experiment. From these experiments came the taper bore weapons, the Panzerfaust & Panzerschreck, and the recoilless weapons.
By the end of the war they were fielding 128mm A/T guns, that while of excellent performance, were big, unwieldy and difficult to hide.
The Russians found that their high velocity 76.2mm field gun made a good tank killer.
The British gradually progressed from the 2 pdr, via the 6pdr (57mm) to the 17pdr (76.2mm). The 25pdr field gun was also issued with an AP shell which was used on occassion to good effect.

The British 3" AA gun was deployed on rare occasions as an A/T weapon. During the defence of Calais several of these guns played a key role in the defence.

One has to wonder at what the German tank crews in 38t's and Pnz II felt when coming under fire from such a lethal weapon.

I would imagine at anything lower than 1000 yards it would probably just go straight through!
Rather like some of the British Cruisers used in the Desert when up against an "88", but not the Matilda, which the 88mm could pierce even at long range, but lacked the momentum to get out again, so just rattled around inside - nasty!

Later in the war some 3.7" guns were fitted with 'open' sights for use in the ground-fire role, but not many. It made a lethal anti-tank weapon but the carriage design and control layout ( the trainers face the breech, not the muzzle as in most artillery pieces) didn't favour it's use for this purpose. The usual short-sightedness of 1930's high command didn't see past the 2pdr but if only ..................Hitler's panzers may have met their match so much sooner.

Early war German tanks were quite thinly armoured, they lost more tanks in Poland than they ever publicly admitted.
I suppose that after Dunkirk we were in extremis as regards equipment so the priority was to replace what we'd lost rather than worry to much about upgrading. The 2 pdr guns mounted in the Matilda and the cruiser tanks were easliy coping with the rather rickety specimens the Italians were putting up against them in Africa. The Matilda was "Queen of the Battlefield" in 1940. The limiting factor in British armour was that the turret ring was too small for anything bigger requiring a completely new design.
What really pressed tank & anti-tank development was the Russian campaigns. Even pre-war a visiting Soviet team refused to accept that the PzIV was the Germans largest tank, this should have told them something. The Germans had nothing to deal with the T34 & KV1, except the "88". The Pak35/36 was ineffective even at point blank range, and was nicknamed "Doorknocker".
The 50mm Pak38 was rushed into production, and while an effective weapon, it was not really until the issue of the 75mm Pak40 that German infantry units had an A/T weapon that could stop Russian tanks at a distance.

The 3.7" gun even in its mobile form was much heavier than the 88 and could never have been used in the same way. Plus it had a more important role in shooting down aircraft, which is what it was meant for. Defending supply lines and ports is more effective than knocking out the odd tank

Much of myth of the 88 is just myth, most tank-killing was done by 50mm and 75mm guns, and in Africa by ex-Russian 76.2mms.

The real problem with the 2pdr wasn't the lack of HE fire it was its immobility. In action the wheels were removed and the crews couldn't just pick it and trundle it along like the German gunners with their 37mms

Wasn't the Allied Bofors AA gun (90 MM?) also used as anti-tank?

As a matter of fact it was, the best known example is the 90mm gun mounted on the M36 Jackson TD. This was a direct modification of the gun and mount to fit on a tank destroyer chassis.
BTW are you the Hiram Sedai from the Combat Mission forums?

The M36 Jackson? wait...M18 Hellcat?

Why, yes...yes I am.

The Bofors was a 40mm weapon and was employed against ground targets on numerous occasions.
I don't know that they were issued with any special AT ammo though.
My late father told me the story of a couple of Bofors guns holding up the Japanese advance in Malaya (as was) in 1941 - they held their fire until the leading armoured cars crested a hill then both let fly and brewed up the enemy cars.
My guess would be standard AA ammo might work against the thinly armoured early war stuff, but only give the crew of a King Tiger a bit of a worrying headache

acav out