Today’s invention is a way to boost the speed of a tank.
The vehicle in question carries a number of shells containing solid rocket propellant. This would be specially formulated to allow relatively slow-burning, sustained-thrust output.
When an extra burst of acceleration is required, the tank’s main gun is rotated to point behind it and a series of these special shells is fired. The resulting exhaust from the gun barrel provides enough drive to eg force a tank through some barrier or out of boggy terrain.