[1] 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 (83.8 mm) gun.

This remained the armament in all the models, although the latest version, generally called the Mk III, had limited elevation.

[2] Birch Guns were used in the Experimental Mechanized Force manoeuvres of 1928, but by 1931 they had been removed from service and political pressure was applied to prevent any plans to complete the third revision of the weapon.

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 Force undertook various experiments in mechanized warfare combining tanks and infantry with their own motorised transport.