The term “1959 EMU” defines a range of four classes within the Mark I electric multiple units which shared a common design of their cab ends that was designed in view of a more aesthetically pleasing appearance. Each class was designed for a different area of operation. They shared some electric equipment with the previous EMUs and all had slam doors in each compartment. With two to four cars per set, all had one car that was powered on all four axles with traction motors of different manufacturers and power ratings.

The class 304 consisted of 45 four-car sets which were designated AM4 before the introduction of the TOPS classes. The classes 305, previously called AM5 and 308, previously called AM8, both consisted either of three or four cars each. The class 305 numbered 71, while the class 308 numbered 45. They were refurbished in the eighties and part of them even got gangways between the cars. While the 304 and 305 were withdrawn in the nineties, the 308 was only withdrawn in 2001 with one set being preserved.

While the others operated under 25 kV AC, the class 504 was built for the unique system with a 1,200 V DC side-contact third rail. This system was only used on the Bury Line between Manchester and Bury. It was also the only of the four classes that only consisted of two cars, with less powerful motors in the powered car. All 26 were withdrawn in 1991 when the Bury Line was converted to the Metrolink light rail system. Of two sets which were selected for preservation, only one still exists today.