In the early 1950s, virtually all BR passenger services were either 1st and 3rd class, or 3rd class only. An exception was the Southern Region boat trains, which carried 1st, 2nd and 3rd class passengers, in order to correspond with Continental ticketing arrangements. These “genuine” second class carriages were therefore built to bring more modern stock to these services. Seating was in eight 2+1 bays with tables, but these were omitted in the fourth bay due to the entrance doors.
In 1956, second class was abolished, and the existing third class renamed second class. As D90 had insufficient seats to be used as second opens they were reclassified as FO and all had been relabelled by 1959. Then in 1963 seven (3501/2/9/10/1-3). were designated as RUO. This was a short-lived experiment as by 1965 all were back to FO, with 3501/2/10 spending some of 1964 as RFO. Other than labelling there was no change to the vehicles. The first withdrawals came in 1964 when 3500/3/5/8 were transferred to departmental use. All others except 3512-4 were withdrawn between 1967 and April 1969. The survivors were transferred to the Eastern Region in May 1969 and may have run another couple of years, but had definitely gone by the end of 1972.