British Rail Class 377

British Rail Class 377 Electrostar
A Southern Class 377/1 at Hastings
The interior of a Southern Class 377/4
In service	May 2003 – present
Manufacturer	Bombardier Transportation
Built at	Derby Litchurch Lane Works
Family name	Electrostar
Replaced	Class 319 Class 421 Class 423 Class 455 Class 456 Class 313
Number built	211 units (excluding 28 375/3 conversions)
Successor	Class 700 (Thameslink)
Formation	377/1/2/4/5: 4 cars per unit (DMOS-MOSL-PTOSL-DMOS) 377/3: 3 cars per unit (DMOS-PTOSL-DMOS) 377/6/7: 5 cars per unit (DMOS-MOSL-PTOSL-MOS(2)-DMOS)
Owner	Porterbrook
Operators	Southern 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)
Traction motors	4–8 × 200 kW (270 hp)
Power output	1,200 kW (1,600 hp) (377/1, /2, /4, /5) 800 kW (1,100 hp) (377/3 only) 1,400 kW (1,900 hp) (377/6 and /7)
Electric systems	750 V DC 3rd rail 25 kV 50 Hz AC Overhead lines (377/2, 377/5 and 377/7 only)
Current collection	Contact shoe Brecknell Willis pantograph (377/2, 377/5 and 377/7 only)
Coupling system	Dellner
Multiple working	Within class, Class 378 and Class 379
Track gauge	1,435 mm (4 ft 8+1⁄2 in) standard gauge

The British Rail Class 377 Electrostar is a British dual-voltage electric multiple unit passenger train (EMU) built by Bombardier Transportation on its Electrostar platform at Derby Litchurch Lane Works from 2001 to 2014.

The trains work suburban services in South London, and main-line commuter services to Sussex, Surrey, Kent and the South Coast, on which they replaced Class 421 and Class 423 slam-door stock that was more than 40 years old and 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 trains 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 rail crash further delayed this upgrade work, and the new stock did not enter squadron service until 2003.