Birch Gun

Birch Gun Mk II
Mark II Birch Gun in action during British Army manoeuvres
Type	self-propelled gun
Place of origin	United Kingdom
Production history
Manufacturer	Vickers (chassis), Royal Arsenal (conversion)
Specifications
Weight	11.9 long tons (12,100 kg)
Length	19 ft 0 in (5.80 m)
Width	7 ft 10 in (2.40 m)
Height	7 ft 7 in (2.30 m)
Crew	6
Armour	6 mm (0.24 inch) Steel
Main armament	1 × QF 18 pdr 3.30 in (83.8 mm) gun
Engine	1 × Armstrong Siddeley 8-cylinder petrol engine 90 hp (67 kW)
Suspension	Bogie
Operational range	119 miles (192 km)
Speed	28 mph (45 km/h)

The Birch Gun was the world's first practical self-propelled artillery gun, built at the Royal Arsenal, Woolwich in 1925.

Despite proving itself a practical proposition the Birch Gun was never highly regarded by the British High Command, apparently not for any particular defect or lack of capability but an entrenched belief that such an innovation was unprecedented and so at best unwelcome and at worst an expensive and unnecessary indulgence.

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 pdr (83.8 mm). This remained the armament in all the models, although the latest version, usually called the Mk III, had limited elevation. Birch Guns were used in the Experimental Mechanised Force manoeuvres of 1928 but by 1931 they had all been removed from service and political pressure was applied to prevent any plans to complete the third version of this weapon.

It would be a decade before the British Army returned to the concept of tracked artillery, in the middle years of a war for national survival where speed and mobility on the battlefield were not optional, and eleven years before it would once again be equipped with a similarly effective weapon.

The armament for the original Birch Gun consisted of an Ordnance QF 18 pounder field gun (3.3 inch, 84 mm). The mounting and sighting arrangements varied over the various versions but the gun remained the same.

The Armstrong Siddeley engine was only moderately powerful by later standards, an 8-cylinder 90 horsepower unit which gave a maximum speed of 28 mph/45 km/h, however, by comparison with tracked armour of the era – the Medium Mark A Whippet 'cavalry tank' of World War I was only two miles per hour faster – it was considered more than adequate, and had twice the Whippet's range.

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. Improvements included changes to the both gun and (very complex) sighting equipment: the top-mounted recuperator was repositioned below the barrel and a gun shield provided for crew protection. In all five vehicles the gun was pintle-mounted towards the front of the vehicle, and had a 360 degree traverse and a maximum elevation of almost 90 degrees, allowing them to be used as anti-aircraft artillery.