To achieve this, the vehicles were generally heavily armoured to allow them to operate in close concert with infantry even under heavy fire.

It was impractical to build more because their road speed of only 18 mph (29 km/h) was too slow for manoeuvre warfare and their armament of a 3-pounder gun lacked the power to penetrate newer foreign tanks.

[2] The Wall Street crash of 1929 and the Great Depression led to big reductions in the funds made available for the army.

[3] In May 1934, Lieutenant-General Hugh Elles was appointed Master-General of the Ordnance and Brigadier Percy Hobart, the Inspector, Royal Tank Corps, asked Vickers to design a tank for infantry co-operation, that could survive all existing anti-tank weapons and be cheap enough for mass production in peacetime.

The next year, Vickers had a two-man tank design, with a machine-gun and powered by a civilian Ford V8 engine of 70 hp (52 kW).

The prototype of October 1936 weighted 10 long tons (10 t) had a maximum speed of only 8 mph (13 km/h) but carried 60–65 mm (2.4–2.6 in) of armour and was mechanically reliable.

[2][4] The 1935 edition of the War Office publication, Field Service Regulations (FSR), containing the principles by which the army was to act to achieve objectives, was written by Major-General Archibald Wavell, made breakthrough the responsibility of infantry divisions with the support of Army Tank Battalions, equipped with specialised vehicles for infantry-artillery co-operation, the slow and heavy Infantry tanks.

(The codification of the difference between Infantry and cruiser tanks and their functions in FSR 1935, accidentally created an obstacle to all-arms co-operation that lasted long into the Second World War.)

In places lacking convenient terrain features, lines-of-communication troops would also need anti-tank guns and be trained to set up localities suitable for all-round defence[5] The need for economy in the design and production of the A11, which was too small for a radio, led to work on a successor, the A12, Infantry Tank Mk II in 1936.

Vickers and government factories could not take on the work and it was farmed out to a civilian firm, which lacked experience, designers and draftsmen.

The pre-Dunkirk British Army Matilda I had only a single heavy Vickers machine gun, a compromise forced by the lightness of its chassis and its target cost.

As British cruiser tank designs developed into larger vehicles with more powerful engines, they could carry bigger guns and more armour and yet still achieve high speeds.