The Bob was a diminutive steam railmotor: a locomotive attached to a single coach.
Remote controls located at the rear of the coach meant that the vehicle did not require turning.
Old railwaymen claim that it was named after one of the original drivers, while others insist that this was a common term given to many small locomotives.
Another theory is that it relates to the cost of a journey in the early days of the service, "bob" being a slang term for a shilling coin.
The last survivor (it is unclear if this was the railmotor used for the Altcar Bob) was numbered 10617 by the LMS.