The AEC Regent III RT was one of the variants of the AEC Regent III. It was a double-decker bus produced jointly between AEC and London Transport. It was the standard red London bus in the 1950s and continued to outnumber the better-known Routemaster throughout the 1960s.

Associated Equipment Company (AEC) was a British vehicle manufacturer that built buses, motorcoaches and trucks from 1912 until 1979. The name Associated Equipment Company was hardly ever used; instead, it traded under the AEC and ACLO brands. During World War One, AEC was the most prolific British lorry manufacturer, after building London's buses before the war.