Armadillo armoured fighting vehicle The Armadillo was an extemporised armoured fighting vehicle produced in Britain during the invasion crisis of 1940 - 1941 . Based on a number of standard lorry chassis , it comprised a wooden fighting compartment protected by a layer of gravel and a driver ' s cab protected by mild steel plates . Armadillos were used by the Royal Air Force ( RAF ) to protect aerodromes and by the Home Guard . Design . With the Fall of France in July 1940 , the Germans threatened to invade Britain . The British Government made frantic efforts to prepare to meet the threatened invasion . One particular problem was the defence of airfields against airborne troops . An ideal solution to the problem of protecting the open space of an airfield would be to make use of armoured fighting vehicles such as tanks and armoured car s . However , the British Army lacked heavy equipment , having been forced to abandon much of it during the Dunkirk evacuation . An alternative would be an improvised armoured fighting vehicle that did not compete for resources with conventional armaments . The form of vehicle that the Royal Air Force ( RAF ) needed was outlined : The RAF started looking for a suitable vehicle at the end of May 1940 and by 4 June they settled on the design destined to be known as the Armadillo . This vehicle was a flat - bed truck , on the back of which was mounted a box - like fighting compartment . The box exterior was made of thick wooden boards measuring about by and standing high ; inside this was another , similar wooden box about smaller all round ; the gap between the boxes was filled with gravel . This provided protection from rifle and machine gun bullets . The fighting compartment had an embrasure on each side , these were about high by wide and fitted with sliding steel shutters . The fighting compartment had an open top with a beam across it to support a Lewis Gun on a sliding mount . The drivers and the engine were protected by steel plates . Most Armadillos were armed with two Lewis Guns and three rifles . Variants . The Mk I Armadillo was produced with startling speed . Using a wide range of trucks conscripted from civilian service , the first 20 were delivered on 7 June and the complete consignment of 312 vehicles within just a couple of weeks . On 20 June , the Air Ministry ordered another 300 vehicles ; these Mk II Armadillos would mostly be based on a standard Bedford OL 1½ and 3 ton chassis . A later Mk III Armadillo was always based on a three ton chassis , it had a slightly smaller fighting compartment now occupying only the front half of the truck ’ s flat bed . On the rear half of the flat bed , a 37mm Coventry Ordnance Works gun was mounted . The COW gun was a 37 mm clip loaded cannon designed at the end of the First World War for arming aircraft and used between the wars on flying boats . It fired a High Explosive shell at modest velocity , but could be expected to be highly effective in its new role against landing aircraft , airborne troops or light vehicles . Fifty - five Mk III Armadillos were made . The crew comprised two drivers and three gunners . In April 1942 , a small number of Mk IIIs had their shingle protection replaced with plastic armour . Service history . It did not matter that the vehicle was lightly armoured , because the soldiers it was expected to meet would be lightly equipped ; what was of key importance was that the vehicle would survive the bombardment that was expected to immediately precede a landing . Armadillos were to be kept a short distance from the airfield , well hidden and protected but always ready to be called into action . Overweight , the Armadillo was unsuitable for travelling over rough or boggy ground . However , it did not need to travel far or fast , nor did it need to cope with hills ; it could easily move along airfield taxiways and perimeter roads . It was thought that commanders might be tempted to think of the Armadillo as a mobile pillbox rather than any sort of tank or armoured car . To counter such a view , instructions emphasised its use as a mobile unit , not a static fort and it was to be reserved for the defence of the airfield and not given other tasks such as transporting ammunition or being driven off to find parachutists . The Armadillo was withdrawn in mid - 1942 , by which time 877 vehicles had been produced . The surviving vehicles were refurbished for other uses ( some passing to the Home Guard ) , and Humber Light Reconnaissance Car s took over their role .