As my last technical article didn't get me lynched for being terminally dull, here's another one. This is the first of a few articles which come from me visiting the National Archives at Kew. They include amongst other things a new British tank that no-one has ever heard of, and finding out that a weapon that's been a long standing joke for the last 70 years is nothing of the sort. However that is all for the future.

When the British tree was released I immediately noticed that someone had made an error. To be utterly fair though, it is confusing and its something only a native English speaker would pick up on. When you're working on the other side of a language barrier it would get lost in translation. I created a thread on the subject on the EU forums. However I got some stuff wrong.

During the period covered by this game the British used three short barrelled 3.7" guns for close support work. To avoid confusion they named the second one in millimetres, as is common in the British military of the time. The Guns in question are:

Q.F. 3.7-inch howitzer: A World War One gun that was only ever used as a towed artillery piece. Some were still kicking about during World War Two, especially out in the far east.
Q.F. 95-mm howitzer: This howitzer was developed sometime in either 1942 or 1943, it was tested in 1943. It had two versions, as an infantry gun version as well as a tank gun. The weapon itself was a section of 3.7" AA gun barrel, married to a 25 lbr breech block. On the infantry gun version the recoil system was taken from a 6 lbr gun. Although the infantry gun was dropped the tank gun saw service from 1944, its normally very easily identified by the huge semicircular counterweight on the gun barrel.
QF 3.7" tank mortar: This was fitted to a few tanks up until the early years of the war, and its the focus of this article.

Development started in the late 1920's when the British started looking at the problem of anti-tank guns. It was quickly realised that the tanks needed some way of closing with the enemy while not getting killed by the enemy AT guns. The obvious idea was to block the enemies line of sight with smoke. Normally smoke would be provided by artillery, but artillery was relatively imprecise and took time to deploy. What was needed was smoke capability that could be provided organically to the tank unit.

Thus the idea of a close support tank was born. At first there was an idea that the CS tank would be a lighter, less complicated, and most importantly cheaper vehicle which could carry 70 rounds of ammunition. It was sometimes referred to as the "Artillery tank".

By 1929 a gun had been developed to fulfill the role, and was fitted with some work to a Vickers Medium MKI. It fired a 15 lb shell, and to enable a high rate of fire it was given a semi-automatic breech to enable a high rate of fire.
On a normal quick firing gun the breech needs to be manually closed. A semi-automatic breech will automatically close when a shell is inserted. It was found that if this happened and the gunner still had the firing handle compressed the gun would fire... while the loaders left hand was still practically touching the breech. This would have obvious results of a smashed left arm and was therefore considered to be too dangerous.
It was also judged that the rate of fire needed wasn't altogether that high. Firing tests showed that one or two rounds a minute would produce a suitable smoke screen. In one test firing while the tank was moving, 6 rounds were fired over 4 minutes that masked a large area. In another test two rounds screened an area of about 800 yards. Obviously the main concern was the weather conditions which would greatly effect the smoke screen.

The shell itself used charged smoke, which is today known as White Phosphorus. Listed in the archives at Kew you have a list of ammunition. These rounds are simply called Smoke, Charged Smoke and High Explosive. Its important to note that official documents do actually call the shell "HE".
This is where that British eccentricity rears up. The Smoke and Charged Smoke were pretty much identical. Both with the same sized bursting charge and carrying two pounds five ounces of white phosphorus. But what of the HE shell? No one has been able to find examples of a HE round being used from the gun. The simple answer is that the "HE" shell had a slightly larger bursting charge (One ounce twelve drams) for added morale effect on enemy troops. It also only carried one pound eleven ounces of WP. A Royal Artillery officer was invited to to view a test of the shell. His one page report is pretty damning. He explains in no uncertain terms what a bad idea this is. He describes the idea as "laughable".
As yet no-one I know has been able to find any mention of a proper explosive HE shell. It is likely that any mention of a HE shell is just this, an idea.
There's also two marks of the gun. But oddly the mark designation was only used within the Royal Tank Corps to designate between the two guns. This caused all sorts of confusion and reproachful letters between civil servants and military officers.
The unofficial mark system is fairly simple: The prototype weapon with the semi-automatic breech and unique mounting which could only be fitted to a Vickers Medium MKI, was termed the MKI, and the production version the MKII.
By the time the MKII came out the gun had been significantly altered to allow it to be totally interchangeable with the 3 pounder gun then used in the Vickers Medium tanks. All you needed to do was swap out the gun and the range drum. This process took years to perfect, but by August 1931 the first guns had passed proof and two had been issued to the Tank Gunnery School at Lulworth.

And as this article is getting a bit long, part two and the 3.7 inch's service will be next week.

Literally yesterday night, and to late to work into the main part of the article, I found some relevant information to this subject.
There's records of a Medium MKI CS tank being delivered to Lulworth in 1923. Now it could be that this tank had the prototype 3.7" tank mortar. But that would mean it took 7 years before they produced a final report on it! The report on it that I have is dated 1930. It could be that the Government only started looking in seriousness at the CS gun for the Medium MKII, and did development work from there. All the documents I've found so far are dated later than 1928.