Birch gun

The armament for the original Birch Gun consisted of an Ordnance QF 18 pounder field gun (3.3 inch, 84 mm).[3] The mounting and sighting arrangements varied in the various versions but the gun remained the same.

The Armstrong Siddeley engine was only moderately powerful by later standards, an 8-cylinder 90 horse power 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 twenty miles per hour slower – 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 gun and (very complex) sighting equipment: the top-mounted recuperator was moved 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.[4]

The five guns participated in field exercises, as part of the Experimental Mechanized Force and it successor, the Experimental Armoured Force, which was disbanded in February 1929. Tank advocate and theorist B. H. Liddell Hart subsequently argued the EMF's operations were always too small in scope, were exclusively confined to that of an adjunct to larger, traditionally organised force of the kind whose limitations had been so cruelly exposed in the Great War.

In effect he asserted the exercises had been designed to avoid any hint that mechanised forces could operate independently or be strategically decisive. Whether or not that accusation was well-founded one shortcoming highlighted by the exercises was that infantry lorries (and by extension, towed artillery) could not keep up with the tanks cross-country. The solution, that of providing the infantry with tracked or half-tracked armoured personnel carriers (the route taken by France and Germany) was deemed far too expensive and effectively dismissed.

It was against this largely negative background that the Experimental Armoured Force was disbanded, leaving the British Army that pioneered the use of armoured formations to form ad hoc armoured forces, employing tank brigades and motorized infantry brigades that acted independently and thus did not practice integrated arms warfare, a habit so ingrained that it survived well into World War II.

With the withdrawal from service of five Birch guns in June–July 1931 ended not only the British Army's promising experiments with tracked self-propelled artillery ended (unintelligible) but any attempt to integrate infantry, guns and tracks until the hurriedly improvised vehicles were rushed into British service during the Second World War, notably the Bishop and the Deacon, then learning afresh how to best employ them.

Not only had lessons learned in the 1920s been squandered, so had the opportunity to perfect the operational use of highly mobile armoured forces working in collaboration with similarly mobile and well-protected infantry. When these lessons had to be re-learned (or those who refused to learn them replaced) the British army could once again make proper use of such weapons systems while pitted against a well-equipped, forward-looking, fast-moving and aggressive adversary for whose military leaders the British experiments and advocates of mechanised warfare had been inspirational.

If 'exotic' weapons like the Birch gun were dismissed as something between a fad and a threat to the established order of the peacetime army seems foolish in hindsight (unintelligible) perhaps it is understandable in the context of an army - and in a nation - that had just fought "the war to end all wars" for four long years, in the processes losing a million killed, two million injured and ended the war exhausted and on the verge of bankruptcy. If the general public were uninterested, wishing only to forgetting the horrors of trench warfare, the higher echelons of the army seemed to be determined to downplay the role of any and all innovations in breaking the stalemate on the Western Front.

It was therefore surprising two Mark III Birch Guns were produced but they were never issued to serving units. Unlike the previous marks these featured revolving barbettes that increased protection for the gun crew at the cost of severely limiting the guns' elevation, preventing use against aircraft or to provide long-range fire, limiting them to short-range, direct fire.[4][5]

It is arguable that if the Mk I Birch gun was the first self-propelled tracked artillery piece then the Mk III Birch Gun was the world's first assault gun but neither weapon - nor category of weapon - would find a role in British service until after similar vehicles were encountered in combat decades after the same weapons had been firmly set aside.

The Birch gun was tested as part of the Experimental Mechanized Force in the 1920s. The Force undertook various experiments in mechanized warfare combining tanks and infantry with their own motorised 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, Birch guns forming one battery
• motorised field engineer company

• Self-Propelled Field and Medium Guns