The Steam Tank

 As I warned last week, this article is a day early due to me having to go to work tomorrow, and thus won't be able to post.

One of the great things in this pastime is finding an answer to a riddle, and it's even better when it leads to a "you what?!" moment, as you're reading a document in disbelieving awe. For a great many years there has been a picture floating around the internet, namely this one:

As you can see it's a Bren gun carrier with a big gun mounted on it. The gun is a Smith Gun as used by the Home Guard, but no one knew what it was for until now. The best guess was an unknown Home Guard battalion somewhere trying to get themselves an armoured tank destroyer. In fact it was a trial build to test if the gun’s mounting could be married directly to an armoured vehicle. But we're getting ahead of ourselves.

In 1940, the UK was standing alone and in imminent danger of invasion, and so the Local Defence Volunteers were formed. These were soon to be renamed the Home Guard. While we now know that any attempt by Germany to invade Britain would have been crushed in in hours, and was doomed to failure, at the time that piece of information was not widely circulated. This lead to a flurry of home defence ideas, not least of which was getting some armoured vehicles to the Home Guard. In due course a committee was set up on 22nd of August 1940 to study the idea of getting a tank for the Home Guard. The committee started out with the name of "Auxiliary Armour Committee", but was soon changed to a name that gives us a clue as to its purpose. The "Steam Committee".

Yes, the Home Guard tank was to be steam powered, and on consideration this isn't as dumb an idea as it sounds. First of all steam power was still in use in the country in agriculture, although nowhere near as widely as a generation before. That would mean a supply of trained and experienced people would have already been in the ranks of the Home Guard. A steam tank would be heavy, but you don't need to make grand strategic manoeuvres with it as the Home Guard needed to keep it in their local area. Equally you don't need it to be fast for similar reasons, along with its speed fitting in nicely with the concept of the the infantry tank.
Most importantly of all was consideration of the fuel supply. Petrol and diesel was tightly rationed. But the north of England is pretty much a solid lump of coal, which would mean adequate and liberal supply was available to power this Home Guard infantry tank. As a further consideration, the tank was expected to be fighting in the densely populated south of England. City fighting throws up quite a bit of timber from destroyed houses, this, it was realised, could be used as a fuel source. Which would lead to a further cut in the logistics burden.

Not quite agriculture, but the point stands I think.

The Steam Committee then, in early 1941, turned its attention to the tank's armour and nearly got derailed in the process. At first the brand new Churchill tank was suggested for the basis of the tank. But the proposal was brought up short by the Ministry of Supply pointing out that the Churchill was needed for the army, and even though the production capacity still had some slack in it in some areas, other areas such as casting and welding had large bottle necks.
After deliberation the Steam Committee suggested that flat plate be bolted together to form its protection. Bolted plate was vastly easier to produce, especially for a shipbuilding country like the United Kingdom.
Enquiries were made of a small ship building firm called Hills & Smyth Maritime, the company wasn't experienced in Government contracts and eager to help the war effort mistook the enquires as an order and began to produce the turrets with great gusto. However this mistake was spotted after only a few turrets had been built, and production halted.

One of the Hills & Smyth turrets.

You can see from the turret design that the later Churchill MK.III turret owed a large chunk of its existence to this mistake. Another curiosity you can see from the constructed turrets is that the roofs were rather thick. This is because the Steam Committee expected waves of Stukas to be over head and were keen to avoid a repeat of France where the Stukas were credited with huge destruction. Of course again, we now know this was more propaganda than actual effect.

With propulsion and the armour and turret sorted the Steam Committee turned its attention to the gun. The new three inch OSB Mk.I Smith Gun was soon to come into service and was chosen for the weapon, right up until the moment someone asked about the firing mechanism and mount. A Smith Gun was fired by a horizontal handle and with the crewman crouching a bit behind, sort of like a grenade launcher. Tank guns of the period were shoulder shoved like a giant rifle. Manufacturing a new mount would cause further delays so the trial on the Bren Gun Carrier took place to see if the gun could be operated under armour. It was found that it worked perfectly and so plans were drawn up to mount the sights and gun directly onto the back of the turret front.
A curiosity of the Smith Gun is that it's a smoothbore. The Steam Committee even tried out firing rubble with a blank charge to turn it into a giant shotgun. Again this rubble could come from bombed out buildings. From those tests it was suggested that any hard object could be fired, suggestions for appropriate ammo type from a more theatrically minded member of the Steam Committee included the idea that a local carpenter could knock up a giant wooden stake!
These trials with the Smith gun did have one lasting effect. The trials report includes a list of the Home Guardsmen who took part in the trial. On that list was a name that rang a bell, Jimmy Perry. A quick google shows he was one of the writers of the BBC comedy series Dad’s Army. In one of those episodes (“We know our Onions”) a Smith gun is used to fire a barrage of onions with a blank round. Mr Perry did later say that the series was based on his experiences with the Home Guard.

The order form for the armour plate.

As it turned out the Steam Committee delivered its plans and initially production was approved. Time had marched on to June 1941 and the situation regarding home defence had altered significantly, although the order above was issued, it was cancelled within days. With its work done the Steam Committee was disbanded and the people involved moved onto other things. The handful of bolted turrets were used for resistance testing and shot to pieces, and these tests showed the massive flaws of bolted armour, and so some good did come out of the entire project. Even if Home Guard Steam tanks would have been cooler.