"Bubble Car" DMU (Diesel Multiple Unit) class 121 number W55028 gets soaped up for a wash, brush, and rinse at Swanage next to the engine shed. The rotating brushes are on rollers so they may be wheeled clear of the track when not required. With a top speed of 70 mph, slam-doors, and vacuum brakes these DMUs were nicknamed "Bubble Cars" by British railway enthusiasts. I can't see any reason for the name.