British Rail Class 121

Sixteen Class 121 single-car driving motor vehicles were built from 1960, numbered 55020-55035. These were supplemented by ten trailer vehicles, numbered 56280-289 (later renumbered 54280-289).  They had a top speed of 70 mph, with slam-doors, and vacuum brakes.  The driving motor vehicles were nicknamed "Bubble Cars" by some enthusiasts.

121