[2] Mathews and his commercial partner John Goldwell Ambrose had been in the Royal Engineers and had a history of wartime innovation with concrete including pre-cast pillboxes and dugouts during the First World War.

[3] Mathews bought twenty-four old lorry chassis on which to base the vehicles and he made up a prototype to show to local military authorities.

Mathews said: "[mobile] Concrete pill-boxes will never take the place of armoured cars and tanks, but the enemy would find them a serious obstacle.

Many were old and some dated from the First World War period, one had even seen service as a fire engine and some had not even been converted from solid to pneumatic tyres.

With a variety of chassis to work on, Bisons inevitably varied in detail, but were made in three distinct types: Steel was a valuable wartime resource so concrete was favoured for armouring these pillbox vehicles.

[7] Lorries arrived at Concrete Limited's Stourton Works in Leeds, where the original metal bodywork was removed and wooden shuttering formers constructed.

Due to the resilience of concrete some traces of the Bison remain today whereas nothing at all is left of the more readily recycled Armadillo.

Those built on steam wagon chassis coped well with the extra weight once boilers were removed, but were no longer powered.

Despite concrete's poor performance as armour against heavy weapons,[10] they would have been quite adequate to defend against the lightly armed German paratroops who were the anticipated attackers at airfields.

Driven, or towed, to a defensive position they could cover the open space of an airfield where enemy paratroops or transport aeroplanes might attempt a landing.

A complete type 2 Bison, reconstructed from extant parts and a period lorry chassis, can be seen at The Tank Museum, Bovington.

[15][16] On 22 March 1991 the remains of the Bison were taken to the Lincolnshire Aviation Heritage Centre; they still retain traces of camouflage paint, and one of the sections has its original wooden shuttering.