Bison concrete armoured lorry The Bison was an extemporised armoured fighting vehicle frequently characterised as a mobile pillbox . Bisons were produced in Britain during the invasion crisis of 1940 - 1941 . Based on a number of different lorry chassis , it featured a fighting compartment protected by a layer of concrete . Bisons were used by the Royal Air Force ( RAF ) to protect aerodromes and by the Home Guard . They acquired the generic name " Bison " from their main manufacturer . Need . With the Fall of France in July 1940 , the British Government made efforts to prepare for the threatened invasion . One problem was the defence of airfields against airborne troops . An ideal solution for protecting the open space of an airfield was by tank s and armoured cars . However , the British Army lacked heavy equipment , having abandoned much of it during the evacuation of Dunkirk . An alternative was needed which would not compete for resources with conventional armaments . The Bison was effectively a mobile pillbox that could be driven to defensive positions when needed , or even used to block runways against landings . Inception . The Bison was the invention of Charles Bernard Mathews who was a director of " Concrete Limited " . At this time , there were many attempts to improvise armoured vehicles , but Mathews had the resources and experience to take a professional approach . 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 pillbox es and dugout s during the First World War . One of Mathews ' more unusual ideas was to stack piles of football sized concrete spheres on top of air - raid shelters ; the idea was that a bomb would waste its energy scattering the heavy spheres rather than breaking the shelter . Mathews bought twenty - four old lorry chassis on which to base the vehicles and made up a prototype to show to local military authorities . Helpful criticism was forthcoming and Mathews was able to produce a version which met the requirements of the Army . 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 . Their great attraction is that anybody can make them – once he knows how " . Mathews ' company trademark then ( and the company name today ) was a Bison , a name which became a generic label for any of these vehicles . " Concrete Limited " obtained chassis where they could . 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 . Type 1 was the lightest . It had a fully armoured cab and a small armoured fighting compartment roofed with canvas . Type 2 had an armoured cab roofed with canvas and a separate fully enclosed fighting compartment resembling a small pillbox on the back – communication between driver and crew must have been difficult . Type 3 was the heaviest and largest , with a contiguous cabin and fighting compartment completely enclosed in concrete armour . Production . Steel was a valuable wartime resource so concrete was favoured for armouring these pillboxes . Any available lorry chassis was used , although the weight of the concrete meant that only the heaviest of chassis were suitable . Lorries arrived at Concrete Limited ' s Stourton Works in Leeds , where the original metal bodywork was removed and wooden shuttering formers constructed . Within the formers , three sheets of expanded metal were placed as reinforcement and then fast setting , high strength concrete made with high alumina cement was poured in . Characteristic ridges at the gaps between the boards are a noticeable feature . When a roof was provided , this was constructed from pre - cast concrete . The walls were about thick and were found to stand up well to Bren gun and armour - piercing bullet s . It is not clear how many Bisons were produced ; estimates vary between two and three hundred . 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 . The existence of these mobile pillboxes received significant publicity at the time . They were briefly detailed in " The Times " and at greater length in " The Commercial Motor " magazine . Performance . Despite un - reinforced concrete ' s poor performance as armour against heavy weapons , they would have been quite adequate to defend against the lightly armed German paratroops who were the anticipated enemy at airfields . These were emphatically " not " " armoured cars " , but merely a pillbox that could be moved from place to place . It was claimed to travel " at normal lorry speed " but in practice it was primarily allocated to the flatness of airfields . Most had difficulty moving at all owing to their excess weight , poor visibility and reduced radiator cooling . Some broke down completely and were either towed , or abandoned in place . Those built on steam wagon chassis coped well with the extra weight once boilers were removed , but were no longer powered . Extant examples . Bovington Tank Museum . A complete type 2 Bison , reconstructed from extant parts and a period lorry chassis , can be seen at the Bovington Tank Museum . This example is a Thornycroft Tartar 3 ton , 6x4 of 1931 or later . The chassis here was a military forward - control Tartar , used as a 3 ton general service lorry ; military Tartars had one wheel on each side of the rear axles , civilian models had " twin wheels " — two wheels on each side . Access to the rear pillbox is through a hatch cut into the lorry decking . The cab armour is open - topped , and was accessed by climbing over . Early examples used a single rectangular box over both sections , but separate sloping - walled boxes saved weight . Some examples were built with unarmoured cabs , emphasising the limits of their mobility to deployment beforehand . Although attempts were often made to protect the engine and vulnerable radiator , this one has merely a light steel plate over half the radiator and the steering box is still exposed . In period it ' s unlikely that a relatively modern military lorry would have been sacrificed in this way , being too valuable to replace losses after Dunkirk . The museum ' s Bison was built relatively recently , from an original rear pillbox on a different original chassis , with the front cab section being a modern reproduction by the Museum of Army Transport in Beverley . The suspension of this example rests on axle stands to avoid flattening the tyres . Lincolnshire Aviation Heritage Centre . This Bison had been used by the Home Guard to defend RAF Digby . Later in the war , Digby was downgraded and hence the additional airfield protection was not required . It was for a while stored at Ferrybridge , Yorkshire and it was used to defend a roadblock on the A15 just outside of Sleaford . Towards the end of the war it was abandoned in a copse to the side of the A15 near Quarington Lane end . The ensuing years saw it stripped and vandalised until eventually the chassis was converted for use as a farm trailer . In 1988 , the Lincolnshire Aircraft Recovery Group learned of its existence of these remains and research revealed what it really was . 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 .