By the late 1950's, many of the older open wagons and louvre vans were being scrapped. To provide additional capacity, steel bodies were built onto scrapped underframes. The bodies were of a style similar to the meduim size bogie boxvans coded _BB_ at the time.
The original plan was for 500 vans. This was later reduced to 400. The order was stopped at 350 built, but with extra components still left, construction continued until 380 were built.
The prototype van B 1, was unusual in that it featured sheet ends, without the pressings.
By the early 1980's, most were being scrapped with some in use as service vans for the Way and Works Branch.
In later years bodies started to be placed at Train Examiner depots as work sheds.