The tank was made by placing an armored box on top of a tractor -- and by "armored" we mean "made from roofing material." Supposedly, the corrugated surface would deflect bullets by virtue of its curviness. Since they also lacked artillery in any numbers, they outfitted the Bob Semple with as many machine guns as it could hold. Six to be exact.
Unfortunately, that last part meant having to cram at least six people into that piece of junk. One of the machine gunners had to lie on a mattress in the belly of the tank, right on top of the burning hot engine. The other five had to stand on the first one's back, presumably. And then they needed someone else to drive the damn thing. According to Wikipedia, the total crew consisted of eight people.
In other words, New Zealand had all the military acumen of Hobbiton.
The Bob Semple was also extremely top heavy and slow -- it couldn't even change gears without coming to a full stop. Also, the vibrations from the tractor rumbling down the grassy plain caused the machine guns to jam, and when someone managed to squeeze off some shots, they tended to be horribly inaccurate. Though it made up for all that by looking ridiculous.
The New Zealand Army rejected the Bob Semple tank for use in their forces, and the units that had already been built were dismantled ... but not before they were paraded in the streets of New Zealand as a way to boost morale.
The Japanese canceled the invasion when they realized that the island had already been taken by their oldest, and dearest ally: ridiculous robots.