Eighty six 6 car units were ordered with an extra 3 car unit for the Aldwych branch, seventy six of these are needed for peak time operation. The trains usually operate with 2 UNDMs in the middle though 20 units can operate as a complete 3 car unit with 2 DMs at either end however service trains usually contain 6 cars. When the Aldwych branch of the Piccadilly Line was still operating then a single 3-car unit was used on it .
|Number built:||519 (86.5 6-car units)|
|Engine:||4 LT118 traction motors per motor car (630v DC fourth rail)|
|Formation:||Driving Motor (DM)+Trailer (T)+Uncoupling Non+Driving Motor
(UNDM)[+UNDM+T+DM] (some as DM+T+DM)
At 18m long the 1973ts cars are longer than previous tube stock (which were usually around 16m long) this allowed for 6 car trains instead of 7 as was the case before with virtually the same capacity but a reduced cost due to smaller number of bogies, car bodies et cetera . The 1973ts was refurbished by Bombardier in the late 1990s and has regularly been London Underground's most reliable fleet of stock .
The 1973ts is due to be replaced in the Deep Tube Upgrade Programme in the mid 2020s. It is possible that some 1973ts cars could live on to be used to replace the ageing 1938ts/Class 483s on the Isle of Wight Island Line.
|235 at Acton Town|
|Approaching Acton Town|
|157 at Acton Town|
|Another 73ts at Acton Town|
|Passing through Ravenscourt Park|
 Anthony Badsey-Ellis and Mike Horne, The Aldwych Branch (Capital Transport, 2009) p. 72
 J. Graeme Bruce, The London Underground Tube Stock (Ian Allan, 1988) p. 114
 John Hawkins, "LU Train Reliability", Underground News No. 644 (August 2015), p. 458