Although these coaches were in production for a relatively short period they came to be as much recognised as the earlier Gresley designs. They had steel flush sides, straight roof, an internal arrangement whereby no passenger had to walk past more than two compartments to reach an exit door, but in a reversion to earlier practice on this and other railways, no cross vestibules at the ends of the coach. The graceful oval windows were distinctive. Those built in 1946/7 had square cornered windows; subsequent batches had rounded corners to prevent corrosion. Reinforcing frames (Comet C61) were fitted to the square cornered carriages.
The coaches entered service on premier routes on the LNER. Interchanging of stock in Scotland led to them being found on the West Coast main line also.