Bob Semple tank The Bob Semple tank was a tank designed by New Zealand Minister of Works Bob Semple during World War II . Originating out of the need to build military hardware from available materials , the tank was built from corrugated iron on a tractor base . Designed and built without formal plans or blueprints , it had numerous design flaws and practical difficulties , and was never put into mass production or used in combat . Despite this , it has become something of an icon of the New Zealand ' do it yourself ' mentality . Design and construction . New Zealand , like its neighbour Australia , had no indigenous armoured fighting vehicle industry . It was expected that armoured fighting vehicles would be provided from the UK . Australia and New Zealand did have some heavy industry that could be turned to the production of armour and armoured vehicles but little had been done . The idea of mechanising the New Zealand Army had been suggested before the war but there hadn ' t been much progress . The use of the US Disston " Six Ton Tractor Tank " a 1937 vehicle constructed of an amoured box on a Caterpillar Model 35 chassis which had been sold to Afghanistan and China was suggested . New Zealand had built some improvised armoured trucks and unable to get any tracked carriers from Australia were building their own with armour plate imported from Australia . After the Fall of France in mid - 1940 , and the loss of most British tanks there , there was no likelihood of production being spared for New Zealand . Rather than obtain the armoured superstructures from the US , it was felt they could produce their own using local materials and resources . It was decided that a ‘ tractor - tank ’ would be an adequate design , as if the need for defense arose , a large tank superstructure could be bolted upon a tractor base within a few hours , allowing for quick transformation and deployment of the tanks . The first ( mild steel ) prototype was built on Caterpillar D8 , a type which was readily available . A lack of weapons meant that it was equipped with seven Bren machine gun s - two in the sides , three facing the front , one in the turret and one at the rear . The vehicle was very tall at 12 ft ( 3 . 5 m ) and performance was poor . Due to the lack of armour plate , corrugated ( manganese ) plating was used in the expectation it would deflect bullets . The crew of eight included one gunner who had to lie on a mattress on top of the engine to fire his Bren gun . The tanks were constructed without the use of any formal plans or blueprints . Working from an American postcard depicting the conversion of a tractors to a ‘ tractor - tank ’ , Bob Semple and TG Beck ( Christchurch District Works Engineer ) , improvised the design of the tanks . Using resources available to Bob Semple as Minister of Public Works , the tanks were quickly produced in their Christchurch workshops . The intention was to disperse the hulls at locations ready in case of a Japanese invasion at which point they would be mounted on tractors for use . The idea was discarded after the tanks attracted public ridicule . Handling and performance . Due to the limitations of requirements and resources , the tank was a functional failure . By using a large tractor as a base , and bolting on a hastily designed and poorly constructed tank superstructure , the resultant tanks were inadequately armored , extremely heavy ( 20 - 25 ton ) , unstable , restricted by tractor gearing to slow speeds , and had to stop to change gears . Furthermore , due to the shape of the underlying tractor and undue vibrations , shooting from the tank was both difficult and inevitably inaccurate . Final result . In the end , due to their impracticality , the tanks were rejected for use by the New Zealand Army , dismantled , and restored to their previous state as tractors . Built during the war hysteria , these tanks were a civilian effort to design and create a means to protect New Zealand . In doing so , the tanks arguably showed a self - reliance and vigor in the nation , uplifting their morale . Used mainly for processions , these tanks were warmly received in Christchurch , Auckland and many other parts of the country .