Class 438 4-TC

In the 1960s BR Southern Region wanted through electric services from London Waterloo to Weymouth, the problem being however that the line had only been electrified as far as Bournemouth in 1967. Instead of having a loco hauled service all the way Southern Region used its typical ingenuity to come up with a novel solution [1][2]. A powerful EMU was developed (4-REP) which propelled 4-TC (Trailer Control) rakes (basically rebuilt Mark 1 coaches with driving cabs at either end) as far as Bournemouth. Then a modified Class 33/1 diesel locomotive with high-level control pipes would propel the 4-TC(s) the rest of the way to Weymouth (the return trip being the opposite way around).

4-TCs could also work in multiple with Class 73/1s and Class 74s in a push-pull manner using the twentyn seven-wire EPB control system [3]. If other (incompatible) locomotives were used then the 4-TCs were plain hauled stock.

Information
Number built: 126 (28 4-car sets, 3 3-car sets, 2 spare vehicles plus 3 later additions)
Built: 1966-7, 1974 (rebuilds from Mark 1 coaching stock)
Builder: BR York
Motor: N/A
Power: N/A
Formation: Driving Trailer Standard Open (DTSO)+Trailer First Corridor (TFK)+
Trailer Brake Standard Corridor (TBSK)+DTSO
3-TC same except for no TFK

Although primarily used on Waterloo-Weymouth services 4-TCs and 3-TCs were also used on elsewhere such as London Waterloo to Salisbury and Clapham Junction to Kensington Olympia services. Electrification finally reached Weymouth in 1988 with the service taken over by Class 442s though the 4-TCs remained in service until 1992.

The 3-TCs were augmented to four coach sets in 1974 by adding the missing TFK [4]. The 4-TCs were Class 491 and the 3-TCs Class 492 under TOPS though later on all were reclassified as Class 438 [5].

A number of vehicles have been preserved including two complete 4-TC sets, one of which is owned by London Underground and carried a "faux teak" vinyl livery for operation with preserved locomotives for a time though is now in London Transport red.
The LU 4-TC set in current London Transport red

The LU 4-TC in the former faux teak livery

Connecting up to 68 025

More familiar 4-TC motive power, a Class 33

The LU 4-TC with a Class 66

The LU 4-TC at Kidderminster SVR

[1] Colin J. Marsden (ed.), "4-REP, 3-TC, 4-TC", Modern Locomotives Illustrated No. 220 August-September 2016 (BR Southern Region Electric Multiple Units) p. 38
[2] John Glover, BR Diary 1958-1967 (Ian Allan, 1987) p. 120
[3] David Brown, Southern Electric Vol. 2 (Capital Transport, 2010) p. 208 
[4] Brian Haresnape & Alec Swain, Third Rail DC Electric Multiple Units (Ian Allan, 1989) p. 67
[5] Colin J Marsden, DMU and EMU Recognition Guide (Ian Allan, 2013) p. 375