 S T D Motors chose to enter the large commercial vehicle market in the late 1920s, and once established they made petrol and diesel buses and electrically powered trolleybuses and milk floats.Commercial Vehicles became a separate department of Sunbeam in 1931.Ownership switched from S T D Motors to Rootes Securities in mid-1935, and later that year their Karrier trolleybus designs were added to Sunbeam production lines.