The initial order, dated 16 May 1930, was for 44 units but this was later cut to 33 units when plans to run a semi-fast London - West Worthing service were dropped. (The underframes for the extra seven units were already built so were used instead for further suburban units). The two end cars of the 4-Lav units were third class 70 seater motor driving brakes, and between them there were two non-driving composite first and third class trailers with compartment layout. One trailer was an 80 seater and the other was a 54 seater with a side corridor. A partition separated the first class compartments from the thirds in this car and there was a lavatory at each end. Units weighed 139 tons and were 256' 9" long and when delivered seated 70 first and 204 third class passengers.

Several units were damaged by enemy action during WWII, but none too seriously and all quickly repaired. Only serious accident resulting in a vehicle lost was the South Croydon crash in October 1947 after which 2926 ran with a 2Hal motorcoach for the rest of its life. In later years the amount of first class seating was reduced, the units then seating 46 first and 234 third (subsequently second).

Though most duties were on the main Brighton line, working in conjunction with 2-Bil, 2-Hal and 4-Sub units, they also had regular workings eastwards to Ore and westwards to Littlehampton, also between Three Bridges and Horsham. For many years they ran a late evening service from London Bridge to Dartford, returning early the next morning, in order to put a pair at Slade Green Depot each night, as this is where all their electrical and bogie overhauls were done. Main body overhauls were dealt with at Lancing (along with accident damage) whilst all routine maintenance was carried out at Lovers Walk Depot, which was where the whole class was always based.

Late in life units gained yellow cantrail markings for first class and air horns replaced their whistles. Three (2921/31/50) got full yellow ends but all were withdrawn still in green livery. These units served the Brighton line well and lasted until the majority were replaced by the far less comfortable 4Vep units in 1968. Just six units, 2923/24/28/39/49/50, lasted into the following year though these were all withdrawn on 5 April 1969 and the last units were scrapped by August of that year. During their last years in traffic they were frequently to be found sharing the hourly stopping services from Victoria and London Bridge to Brighton via Redhill (giving a half hourly service south of East Croydon) with 2Bil units, and were, additionally, the mainstay of the hourly semi fast Victoria to Brighton service.