Mark III (A1) Peacekeeper
From Halopedia, the Halo wiki
Mark III [A1] units are usually equipped with a large riot shield and a low-pressure autocannon that can fire a variety of riot-control munitions.
The Peacekeeper was first visualized by MEGA Brands Halo Toys as the "Sector 12 Police Cyclops". The vehicle was considered a separate entity to the Mark III described on Halo Waypoint until February 2020, when Jeff Easterling confirmed the connection.