Class 321 are 25 kV AC 4-car electric units built between 1988 and 1991. They are rated at 1072 kW, 1437 hp and have a top speed of 100 mph, 162 km/h. 321/4 have a larger first class accommodation than 321/3.

321417 at Watford Junction on Friday June 11th, 1999.