In December 1949, Queensland Railways placed an order with Commonwealth Engineering for eight M series carriage sets totalling 99 carriages to introduce air-conditioned rolling stock to its long distance services. In addition QR's own North Ipswich Railway Workshops built a train. The carriages were designed to travel to all parts of the system with a maximum axle load of nine tons, which was a challenge for the dining cars. New features included showers in the sleeping cars, roomettes in first class and head end power cars, especially necessary where trains may be delayed by floods or other events, as was often the case.