In 1919, Frank Barnwell entered discussions with the Royal Mail Steam Packet Company about the feasibility of using flying boats as auxiliaries to ocean liners.
As Bristol's heavy bomber, the Braemar – the progenitor of the Pullman – had originally been designed to have a central engine room with driveshafts to wing-mounted propellers, the Pullman seemed a suitable candidate as a testbed for the installation of a steam turbine engine room.
The powerplant was to consist of two 1,500 hp (1,120 kW) steam turbines of the Ljungstrøm type, with closed-circuit high-pressure flash boilers.
[1] The unprecedented 3,000 hp (2,240 kW) would be delivered though driveshafts and clutches to four-bladed tractor propellers mounted on each middle wing (the Braemar/Pullman/Tramp family were triplanes).
The main problem turned out to be designing a reliable lightweight closed-circuit boiler and condenser.