The Smith Gun actually looked like a real field artillery engine. It was developed by the chief engineer of the Trianco heating appliance company under his own initiative: the cynical called it the ‘Triang gun’ after the toy company.
It was a 3-inch, smooth bore howitzer with solid metal wheels that – with its limber – was light enough to be towed behind a civilian car. The gun was simply upended on one of the wheels for firing.
It had an effective range of about 500 yards and could discharge HE and AT rounds. It was strangely popular, despite an appalling safety record. The exact number manufactured is uncertain but seems to have been 3,000–4,000.