Similar in external appearance to the 9 compartment coach with the exception that there is a toilet compartment in the middle, this coach, as the name implies is open with access from both sides to the toilet. However to maximise capacity there is no connection between coaches. These coaches were for the commuter traffic into cities but for passengers with a longer journey time and hence the need to use facilities. The open nature and lavatory installation meant that these carriages carried 20 fewer passengers than the compartment version.
The Railway has 2 such carriages which finished their main line lives working out of Kings Cross on outer suburban routes and are regularly to be seen on the service trains.