Panzerserra Bunker- Military Scale Models in 1/35 scale: agosto 2025

Birch gun Mk.II - 18 pdr. self propelled artillery

His Majesty's Gunners!!!

Today we are going to talk about the Birch Gun 18 pdr. SPG, an interesting and early attempt at a self-propelled gun. Created in the 1920s, it mounted a standard QF 18-pounder field gun on a Vickers Medium Mark II tank chassis. The idea was to create a fast, mobile artillery piece that could keep pace with advancing troops, a rather revolutionary concept for the time. And although they could elevate their main gun to almost 90 degrees, they were not designed to serve as anti-aircraft weapons. Only a few of these vehicles were built, and these self-propelled artillery pieces never saw combat.

Captain Darling was completely wrong....

History

It can be said that the British were the precursors not only of tanks but also of the concept of self-propelled artillery. The Gun Carrier Mk.I is the greatest example of this, being a highly advanced weapon for its time.

Gun Carrier Mark I carrying a 60-pounder gun

Gun Carrier Mark I carrying a 6-inch howitzer

Besides being an SPG, it was also a gun carrier, meaning the guns ( 6-inch howitzer or a 60-pounder gun ) could be unloaded from the chassis, allowing both the gun and the chassis tractor to operate independently.

British Gun Carrier Mark I self-propelled gun
chassis only - IWM (Q 71284)

After World War I, the military focused more on the use of towed artillery, but the British did not forget about SPGs. In the early 1920s, an experimental line of these vehicles was created, like the Light Artillery Transporter, culminating in the lineage of the Birch Gun.

Light Artillery Transporter 18 pdr.
The first British SPG created after the First World War.

The Birch Gun was the first practical British self-propelled artillery gun, built at the Royal Arsenal, Woolwich in 1926-1927.

Named after General Sir Noel Birch, who was Master General of Ordnance at the time, the Birch gun comprised a Vickers Medium Mark II tank chassis originally fitted with a QF 18-pounder Mk.IV (83.8 mm) gun.

Lieutenant-General Sir James Frederick Noel ('Curly') Birch

GBE KCB KCMG

font: IWM

Vickers Medium Mk II tank

right front view

font: IWM MH 11707

QF 18 pdr. Mk. IV field gun

The initial Birch Gun prototype was sent for field testing, and a series of improvements were made as a result.

Birch Gun prototype , armed with 18 pdr. Mk.I
left side view

Birch Gun prototype , armed with 18 pdr. Mk.I
front view

Vickers received an order for four 18-pounder SPGs in September 1925. They were ready in about a year. The vehicle weighed about 12 tons and had 5 mm of armor.

Compared to the Birch gun prototype, the SPG now had a large shield that protected the crew from the front. A traverse lock was also added. The gun elevation increased to 80 degrees, which improved the Birch Gun's capabilities as an anti-aircraft vehicle. The ammunition magazines held 80 rounds and were stored securely inside the hull.

Continued operational testing in the late 1920s demonstrated the vehicle's versatility and robustness, as well as the superior performance of a self-propelled artillery vehicle over a standard artillery piece towed by a tractor. The SPGs' maneuverability was very similar to that of tanks.

Operational tests carried out on Salisbury Plains in mid-1926.
In a direct comparison between guns towed by artillery tractors
and self-propelled guns, AP artillery proved to be more
maneuverable, versatile, and faster.
In the foreground, a Birch gun is moving, while in the background,
we see tractors towing 18-pound pieces.
Frame taken from a British Pathé film

Sequence of 3 frames from a British Pathé film showing a battery
of Birch Guns overtaking a tractor with its artillery piece and ammunition trailer.
The future overtaking the past...

The production vehicles were sent to the 20th Field Battery of the 9th Field Brigade, Royal Artillery, where they proved their worth and operability as a tactical weapon.

Birch Gun 18 pdr. with gun lying in its travel lock - 1926
front right view

While its performance was encouraging, the Birch Gun had its problems. Although its designers attempted to reduce the vehicle's height as much as possible, its center of gravity was relatively high for a 12-ton vehicle. Because the 18-pounder gun had much greater recoil than the standard 3-pounder (47 mm) gun of the Medium Tank Mk.II, the vehicle's chassis had much more difficulty absorbing the resulting forces, shaking considerably upon firing, especially with the gun firing at 90º drift.

Birch Gun Mk.II firing the 18 pdr. back.
Note the positioning of the crew, almost completely exposed.
British Army manoeuvres.
20th Battery, 9th Field Brigade, Royal Artillery - 1926

The armor, while superior to that of the prototype, was still insufficient to be effective when engaged against ground targets. The crew huddled behind the shield, which rotated with the gun, but were left unprotected from attacks from the sides and rear. The driver's situation was poor too, as he was protected only by a small deflector vertical plate installed to the left of his exposed combat position.

Armament

The armament for the operational Birch Gun consisted of an Ordnance QF 18 pounder field gun (3.3 inch, 83,8mm). The mounting and sighting arrangements varied in the various versions but the gun remained the same. There was no secondary point defense weaponry, nor any provision for it.

Birch Gun 18 pdr. with the gun at full elevation - 1926
front right view

Birch Gun 18 pdr. with the gun in lying position - 1926
rear left view

Powerplant

The Armstrong Siddeley engine was only moderately powerful by later standards, an 8-cylinder 90 horse power unit which gave a maximum speed of 45 km/h, however, by comparison with tracked armour of the era – the Medium Mark A Whippet 'cavalry tank' of World War I was twenty miles per hour slower – it was considered more than adequate and had twice the Whippet's tank range.

Use

The Birch gun was tested as part of the Experimental Mechanized Force (EMF) in the 1920s. The Force undertook various experiments in mechanized warfare combining tanks and infantry with their own motorised transport.

The components of the EMF were:

reconnaissance group with tankettes and armoured cars
battalion of 48 Vickers medium tanks
motorised machine gun battalion
mechanised artillery regiment

including one battery of Birch guns

motorised field engineer company

Birch gun - Demonstration by British Army for prime ministers
from Empire countries in UK for Imperial Conference
Camberley, Surrey - November 1926.

Birch Gun Battery during field maneuvers
Camberley, Surrey - November 1926.

Birch gun- Aldershot Grand Review
Aldershot, Hampshire, England - summer 1927

Birch gun speed - Aldershot Grand Review
Aldershot, Hampshire, England - summer 1927

Birch Gun climbing an obstacle at
Wool, Dorset - England - February 1927.

Despite the problems arising from a weapon still new in its principles, the Birch Gun concept was sound. Had the British persisted in developing the weapon, they would have had a family of highly mobile SPGs capable of fighting alongside tanks and providing immediate fire support by the early 1930s.

But unfortunately, as in many Allied forces, the British army was dominated by conservatism. And let's not forget that a towed gun and a tractor were much cheaper than an armored SPG. Recalcitrant artillery officers also countered that a traditional gun was lower and that preparing and camouflaging its position was much easier. In the end, these arguments from opponents of artillery mechanization prevailed, even though it was logical that the two forms of artillery, towed and self-propelled, complemented each other.

The Birch Gun program began to flounder in 1927, not because of its own shortcomings, but when Sir Birch left his post and transferred to Vickers. He was replaced as Master-General of the Ordnance by Lieutenant General Webb Gillman, a much more conservative officer. His view was that the correct way to move artillery was through the use of tractors, whether wheeled or tracked.

Major-General Sir Webb Gillman

KCB, KCMG, DSO

font: IWM

The High Command's discreet but firm opposition to the SPG principles and the dissolution of the Experimental Mechanized Force in early 1929 marked the end of the Birch Gun program. Its more advanced version, with greater crew protection, the Birch Gun Mk.IE( 1928), saw only one build, which was soon forgotten.

Birch Gun Mk.IE prototype - 1928
left side view

Birch Gun Mk.IE prototype - 1928
right side view

This stagnant vision had bitter consequences at the end of the next decade, as the British watched and learned the hard way the Germans' deadly use of artillery that could keep pace with their advancing armor with the same speed and performance as their tanks.

In the early 1940s, work on the concept and development of SPGs had to start practically from scratch, repeating all the same initial mistakes of a new weapon. All these painful stages could have been avoided if the self-propelled artillery program of the 1920s had been maintained, even at the lower speeds and production levels typical of peacetime.

Specs:

Birch Gun Mk II
Type	Self-propelled gun
Place of origin	United Kingdom
Production history
Manufacturer No. built	Vickers (chassis), Royal Arsenal (conversion) 7 (1926-1927)
Specifications
Mass	12,100 kg
Length	5.80 m
Width	2.40 m
Height	2.30 m
Crew	6

Armour	6 mm Steel
Main armament	1 × QF 18-pounder 3.30 in (83.8 mm) gun
Engine	1 × Armstrong Siddeley 8-cylinder petrol engine 90 hp (67 kW)
Suspension	bogie
Operational range	192 km
Maximum speed	45 km/h

Kits:

To build this project, I used a 3D printed kit from MRY-SFW (SS Model), from China (Shenyang, Liaoning). I received the Birch Self-Propelled Artillery kit (#SS35554) in 1/35 scale in a cardboard box, protected by layers of bubble wrap.

SSModel kit box art with Kojak, in my workbench.

The kit is very well printed, with almost no print lines and is extremely spartan, with an assembly sheet for the sub-assemblies (not very detailed, unfortunately) and no decal sheets or accessories.

The assembly sheet for the subassemblies,
with confusing details and very bad paper printing...

All the pieces are on the bench.
As always, I'll use superglue for construction.

The suspension subassembly arrived with substantial longitudinal warping. While it looks bad, this was quickly and easily remedied by dipping the parts in very hot water to soften them and then aligning them on a flat surface, followed by an ice-cold water bath to stabilize the resin. Fortunately, I didn't notice any uncured resin, which is common in these 3D resin kits.

The bent suspension bogies...
Fortunately, easily correctable...

More ugly than important.
Boiling water fixes this quickly...

I discovered a broken track link...

Fortunately, it was facing the lower portion.
The fragment was inside the plastic bag...
The repair was easy, with superglue.

Suspension bogies, after thermal shock with
boiling water - flat surface - cold water.

I used my sanding surface (a sheet of medium and fine grit wet sandpaper bonded with contact adhesive to a 7mm thick glass plate) to grind the chassis base and the bonding surfaces of the suspension bogies.

Flattening the chassis base and the bonding
surfaces of the suspension bogies.

The pins in the sprocket wheels were ground along their
length (yellow arrow) to allow the suspensions to fit
perfectly to the side of the chassis. To glue the bogies to the chassis,
I used superglue gel, which allows for positional adjustment (green)

I added a thin sheet of plasticard (0.5mm thick) to provide a bonding support between the base of the car chassis and a thin finishing sheet on the suspension bogie.

Plasticard reinforcement (0.5mm thick)
for better gluing support (yellow arrow)

When gluing the two suspension bogies to the chassis, I placed a styrofoam block under the chassis to provide stable and aligned support during the gluing process. As mentioned earlier, I used gel superglue to allow for slight adjustments in the suspension positioning. To avoid errors, I glued the bogies with minimal contact areas to check and stabilize the positioning of these parts. After checking the chassis alignment relative to the ground, I "sewed" the bogies together with regular superglue, infiltrating the liquid between the chassis and the bogie contact surfaces. The bond was extremely rigid and perfectly aligned.

Suspensions in position.

Front view of the kit, with front panel ready to be glued

Rear view of the kit, with rear panel ready to be glued

Done!

Adding toolboxes over the top of the left fender

Gluing the 18-pound howiter and its shield to the edge of the chassis bore is somewhat empirical, based on the poor instructions provided. My solution was to glue the cannon base to the edge of the combat station (I chose the 12 o'clock position to position my gun), supporting the base of the gun on a popsicle stick as a template for gun alignment. Then I inserted the shield into the cannon and glued the risers into position, using the same popsicle stick as a horizontal reference. If you follow the instructions, you'll end up falling off a cliff...

Gluing the howitzer and then the front shield.

Close up of the 18 pdr. gun

Now, what I consider the biggest problem with this kit: the main armament. When I saw the kit in my hands and looked at the gun's injection quality, my first impression was that the guys at SS Model used the 25-pdr. as the main weapon for the Birch gun kit, mainly due to the differences between the kit's 18-pounder and the one in the original photos. Looking at the photos between the kit gun and the original photos (look the pic, below), the details that draw the most attention are the positioning, size and position of the elevating and transverse hand wheels (red arrows in the photo below), the sighting device (green), the shape of the breech (blue), the abscence of the rear extension of the cradle (purple) and the presence of the range scale cone (white).

Discrepancies between the kit's 18-pdr.
gun and the actual vehicle's.

What struck me most was the conical piece (range scale cone or Probert scale cone) installed on the left rear of the gun, so typical of 25-pdr. but absent from the 18-pdr. The range scale cone is as characteristic and identifiable to the 25-pounder as the hemispherical muzzle brake is to the 17-pounder.

The positioning, size and position of the elevating and transverse hand wheels
(red arrows) in the 25 pdr. gun and the kit gun. Notice also the
short cradle (orange) and the range scale cone (green),
all typical features of the 25 pdr.

The Probert range cone in details.

In short, the kit presents a gun with many of the details of a 25 pdr, rather than an 18 pdr. I was wondering why SS Model chose to include such wrong details in their kit, since the photos of the Rael model are available on the Internet for anyone who wants to see them and my opinion is that the SS Model kit was entirely based on the rendered images from the online game World of Tanks, since the similarity between the game's drawings and the SS Model model is simply complete...

Birch gun from World of Tanks.
Notice the physical similarity between the game
designs and the SS Model kit.
left front top view

Birch gun from World of Tanks.
Notice the physical similarity between the game
designs and the SS Model kit.
right front view

Birch gun from World of Tanks.
Notice the physical similarity between the game
designs and the SS Model kit.
Notice the rear gun details

But continuing the construction of the kit...

Gun in position

Notice the details of the rear sight of the breech of the "18 pdr."... Very similar to that of a 25 pdr.... and identical to the game renders.

Rear view of the 18-pdr. gun kit

Using a dental curette and a steel ruler, I carved grooves to delimit the rear engine access panels, as well as scratch-cutting the hinges and handles on these same panels (yellow arrows, below), to give the model a little more authenticity.

Adding details to our Birch gun.

The wooden boxes, after being cleaned and their bottoms
sanded and planed, were tested in place. Since they will be painted wood-colored,
they will be installed in the final phase of construction.

I glued the two headlights into place, and almost immediately, while handling the model, one of them broke. They were very prominent, and the resin was very brittle. Before tragedy struck (loss of the part), I decided to cut the resin headlight stems and replace them with copper wire segments of the same thickness. This makes the kit more secure during handling and display.

Headlights in position, before metal graft.

And with that, I consider the kit construction phase complete. As always, I like to make a three-view drawing of a painting and markings guide. I decided not to reproduce the historically accurate markings from period photos, but rather the markings of a vehicle serving with a possible 22nd Battery, 9th Field Brigade, Royal Artillery, in field trials on Salisbury Plains in mid-1926.

Panzerserra Colors & Markings guide

Color base - Dark green with tonal variations
left front view

Color base - Dark green with tonal variations
right front view

While the colors and their tones were drying, I made the decal art, using Corel Draw and my laser printer. As always, I created a white background section (red circle, below) and a section with the unit markings, printed on clear decal segment (blue circle).

Decals in close up
transparent (blue circle) and
flat white, for background (red circle).

After spraying a couple of thin coats of Pledge only to the areas that will receive the decals, I applied the decals. The letter A, the vehicle's code, came from my spare decal box. After the decals were completely dry, I sealed them with another coat of Pledge and sprayed the entire kit with a very even coat of matte varnish.

After the decals and varnishes are completely dry,
painting the tracks with Gun Metal, with a brush and a steady hand...
left front view

Right front view

Rear view

Applying weathering with oil diluted in spirit and other techniques...
Notice the shovel installed on the rear deck, which came from my junk box.

Detailing in the painting...

And after applying a few more details, such as pigments and accessories, I completed this fascinating project, a vehicle that was the precursor to a whole new family of weapons for the British Army, but which emerged very prematurely. It's a shame that SS Model's printed model isn't as accurate as this important artillery piece truly deserves.