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 Britain. Australia[3] 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 without much progress. The use of the American Disston "Six Ton Tractor Tank", a 1937 vehicle constructed of an armoured box on a Caterpillar Model 35 chassis[4] which had been sold to Afghanistan and China, was suggested.[5]

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 America, 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; 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 a Caterpillar D8 crawler tractor, a type which was readily available.[5] The Public Works Department had 81 D8s, and another 19 were available.[2] A lack of weapons meant that it was equipped with six Bren machine guns — one in each side, two 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.[6]

The tanks were constructed without the use of any formal plans or blueprints. Working from an American postcard depicting the conversion of a tractor 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 first tank was quickly produced in the PWD's Temuka workshops. The additional two were built at the NZR Addington Workshops.[7] The first cost £5,902; the second and third £4,323; total cost £10,225 (although the Army was only billed £3,414).[8]

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; however, Bob Semple stood by his design and even stated "I don’t see anyone else coming up with any better ideas."[6]