Diagram 36 carriages ran as a triplet set with a D700 kitchen car (Comet B17BS) and a D56 restaurant second open (B17CS). They were known as Festival of Britain sets when first introduced and ran on premier services. They were branded RESTAURANT CAR centrally in the lower body panel.
Diagram 71 was effectively the prototype open first: experience showed that an additional door each side would be useful, and all subsequent FO diagrams featured this.
Both diagrams were built at York and ran on B1 bogies.