From Halopedia, the Halo wiki
Although anti-heavy armor fire would blow the Cougar away quite easily, this vehicle was highly effective in holding off enemy armored vehicles until slower armored units could arrive at the battlefield. The Cougar had gained infamy in several urban tactical situations prior to the deployments in the war against the Covenant.
It appeared as a somewhat standard armored fighting vehicle with two wheels up front and two pairs in the rear. It bore a small mounted turret armed with two M68 Gauss cannons, as well as a machine gun or grenade launcher on other concept art. There was a windscreen on its forward body, with two side windows to provide a fairly high amount of visibility for the driver, which would have proved useful. It would have been able to reach a top speed of 90mph.
According to Ensemble Studios, the Cougar was cut from the game in favor of other vehicle ideas. Its shape may have proved the inspiration of the SP42 Cobra, as its role in Halo Wars was originally an anti-vehicle unit. The Cougar bears a striking resemblance to the World War II armored car, the M8 Greyhound.