Photograph of Rex as a 55-years-old propulsion engineer in 1974.

When Napier aero engines started to decline in late 1950s he moved to Rolls-Royce working on multitude of engine design including the famous RB211 which later evolved into long-lived Trent family. Here he was photographed with the landing gear of Boeing 747-200 which was to be powered by four RB211 engines - in fact, the B742 was the first commercial aircraft to offer engines from the "big three" manufacturers; Rolls-Royce, Pratt and Whitney and General Electric.

While the RB211 costs higher than its contemporaries the P&W JT9D and GE CF6, It offers better "hot and high" performance than the latters, which is the reason why Saudia and Cathay used them. Qantas operated 747 fleet powered by RB211 burn 7 percent less fuel than its JT9D powered fleet. And most of all, RB211's common exhaust nozzle provide partial internal mixing of exhaust and bypass gasses resulting in quieter operation.