Diagram 56 carriages ran as a triplet set with a D700 kitchen car (Comet B17BS) and a D36 restaurant first open (B17AS). 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 92 was effectively the prototype tourist open third: experience showed that an additional door each side would be useful, and all subsequent TTO/TSO diagrams featured this.
Both diagrams ran on B1 bogies and were reclassified as second class in 1956.