The British Rail

British Rail

British Railways , which from 1965 traded as British Rail, was the operator of most of the rail transport in Great Britain between 1948 and 1997. It was formed from the nationalisation of the "Big Four" British railway companies and lasted until the gradual privatisation of British Rail, in stages...

 Class 933 was reserved for former Southern Region electrical multiple units converted for departmental use. Originally the series was reserved for Mobile Instruction units. In recent years, however, this series appears to have been discontinued.

The Southern Region initially numbered its departmental EMUs in a series between S1 and S101. In 1968, a new series was adopted; 001-099. Existing units were renumbered to fit in that series, which also included other non-passenger stock, i.e. those EMUs converted for parcels traffic. Several of the numbers 001-099 have been reused for different units.
When TOPS

TOPS

Total Operations Processing System, or TOPS, is a computer system for managing the locomotives and rolling stock owned by a rail system...

 class numbers were allocated, these units retained their existing numbers as the last three digits of their new TOPS class number. The table below lists the mobile instruction units allocated Class 933:

Key:	In service	Withdrawn	Preserved	Reclassified	Scrapped

Unit No.			Converted	Use	Former Class	Final livery	Original Formation				Wdn.	Status
TOPS	SR Series	Original					DM	T	T	DM
-	S10 / 053 (1st)	4579	1956	Mobile Instruction	405 British Rail Class 405 Under the British Rail TOPS computer system, Class 415 was allocated to surviving examples of the Southern Railway 4-Sub Class electric multiple units built between 1941 and 1951...	Blue	DS40 ex.8564	DS41 ex.9658	-	DS42 ex.9817	1974	Scrapped (1976)
-	055	4367	?	Mobile Instruction	405 British Rail Class 405 Under the British Rail TOPS computer system, Class 415 was allocated to surviving examples of the Southern Railway 4-Sub Class electric multiple units built between 1941 and 1951...	Blue	975319 ex.10919	975320 ex.10171	975321 ex.11470	975322 ex.10920	?	Scrapped (1987)
-	998	?	?	Mobile Instruction	415 British Rail Class 415 British Rail Class 415 was a suburban 750 V DC third rail electric multiple unit commissioned by the Southern Region of British Railways. Built between 1951 and 1957, it became the most numerous class on the region after the withdrawal of the 4Subs...	Blue	977702 ex.14574	977703 ex.15013	977704 ex.15160	977705 ex.14487	?	Scrapped (1991)
-	999	?	?	Mobile Instruction	416 British Rail Class 416 British Rail Class 416 electric multiple units were built between 1953 and 1956. They were intended for inner suburban passenger services on London's Southern Electric network...	Blue	977688 ex.77111	977689 ex.77106	977690 ex.77102	977691 ex.77103	?	Scrapped (1992)