British Rail Class 377

British Rail Class 377 Electrostar
Southern Class 377/6 No. 377605 at Battersea Park
The interior of a Southern Class 377/6 EMU
In service	May 2003 - Current
Manufacturer	Bombardier Transportation, Derby
Family name	Electrostar
Replaced	Class 319 (Thameslink) Class 456 (Metro) Class 421 (Mainline) Class 423 (Mainline)
Number built	211 units (excluding 28 375/3 conversions)
Number in service	239 units
Formation	377/1/2/4/5: 4 cars per unit (DMOC-MOC-PTOS-DMOC) 377/3: 3 cars per unit (DMOC-PTOS-DMOS) 377/6/7: 5 cars per unit (DMOC-MOS-PTOS-MOS-DMOS)
Operator(s)	GTR Southern GTR Thameslink Southeastern
Specifications
Car length	20.4 m (66 ft 11 1⁄8 in)
Width	2.80 m (9 ft 2 1⁄4 in)
Height	3.78 m (12 ft 4 7⁄8 in)
Maximum speed	100 mph (161 km/h)
Weight	173.6 t (170.9 long tons; 191.4 short tons) (377/1, /2, /4, /5) 133.1 t (131.0 long tons; 146.7 short tons) (377/3 only)
Power output	1.2 megawatts (1,600 horsepower) (377/1, /2, /4, /5) 0.8 megawatts (1,100 horsepower) (377/3 only)
Electric system(s)	750 V DC 3rd rail 25 kV 50 Hz AC Overhead lines (377/2, 377/5 and 377/7 only)
Current collection method	Contact shoe Pantograph (377/2, 377/5 and 377/7 only)
Multiple working	within class
Track gauge	1,435 mm (4 ft 8 1⁄2 in) standard gauge

The Class 377 Electrostar is a British electric multiple-unit train (EMU) built by Bombardier Transportation at its Derby Works, from 2001 to the present. The Electrostar family is the most numerous type of EMU built in the post-privatisation period of Britain's railways.

The class forms the major part of the Govia Thameslink Railway (GTR) fleet for Southern and Thameslink services. They are primarily seen on services in the south of England.

The units work suburban services in South London, and main line commuter services to Sussex, Surrey, Kent and the South Coast, on which they replaced 4Cig and 4Vep slam-door stock which came to end of their useful lives and which did not meet modern health and safety requirements. Built in the early 2000s, the units had a troubled introduction; being fully air-conditioned, their higher power consumption compared to the slam-door Mark 1-based stock that they replaced led to major upgrades being required to the 750 V DC third-rail power supply used in the former Southern region. The collapse of Railtrack following the Hatfield accident further delayed this upgrade work, and the new stock did not enter squadron service until 2003.

Class 377s are fitted with external CCTV. There is a disabled seating area, and both intermediate coaches have toilets. Bodyside power doors are electrically operated, a move away from the air powered systems of previous generation EMUs. Dual-voltage units are fitted with a Brecknell Willis high-speed pantograph, incorporating a pair of aerofoils on the pan knuckle to steady the pan head against the OLE contact wire. The configuration of a 5-car Class 377 unit is: