Although these coaches were in production for a relatively short period they came to be as much recognised as were 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.
Earlier lots to this diagram (Comet E1K, as seen in the photo) built in 1946 and 1948 had square cornered windows, which rapidly corroded in service. A change was made to round corners for these later lots which successfully avoided corrosion.
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.