Birch gun

The Birch Gun was the world's first practical self-propelled artillery gun, built at the Royal Arsenal, Woolwich in 1925. The gun was never highly regarded by the British High Command, purely for prejudicial beliefs and political pressure rather than any real lack of ability. Named after General Sir Noel Birch, who was Master General of Ordnance at the time, the Birch gun had real potential. It was built upon a Vickers Medium Mark II tank chassis and mated originally with the QF 18 pdr (83.8 mm) gun then with a 75 mm field gun. The project was abandoned in 1928 after political pressure killed off any plans to complete the third version of this weapon.

Armament
The armament for the original Birch Gun consisted of an Ordnance QF 18 pounder field gun (3.3 inch, 84 mm). This was changed to the 75 mm gun on the Birch gun Mk II and from then on was able to be fired either at ground targets or in the air-defence role, being given a much higher rate of elevation to be fired at enemy aircraft.

Powerplant
The Armstrong Siddeley engine was modestly powerful. Being only 8 cylinders it could manage 90 hp for a mild 45 km/h top-speed. However, for its time (late 1920s) it was quite fast.

Variants
The initial prototype, the Mark I, made its first appearance in January 1925 and spent the next year undergoing trials and taking part in manoeuvres, mainly with 28 Battery, 9th Field Brigade, Royal Artillery. The lone Mark I was transferred to 20 Battery, 9th Field Brigade RA, who then took delivery of three Mark II Birch Guns in July 1926, followed by a fourth gun in September. This brought the battery strength to five guns, which participated in various field exercises as part of the Experimental Mechanised Force and it successor, the Experimental Armoured Force which was dispersed in February 1929. All five guns were finally withdrawn in June/July 1931, effectively ending the British Army's experiments with tracked self-propelled guns until the advent of various hurriedly improvised vehicles during the Second World War, such as the Bishop, and the Deacon. Two Mark III Birch Guns were produced, but never issued to serving units. These had the guns mounted in revolving barbette-style turrets that increased crew protection but reduced the guns' elevation, so capping their effective range.

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

The composition of the force was:
 * reconnaissance group with tankettes and armoured cars,
 * battalion of 48 Vickers medium tanks,
 * motorised machine gun battalion,
 * mechanised artillery regiment- the Birch guns formed one battery of it
 * motorised field engineer company.