Simplify the following text for a Grade 12 native English-speaking person.
Original: The class was intended to be a modern replacement for the ageing ` first generation ' types in use on the Southern Region of British Railways ( classes 201 to 207 ) but the prototypes built did not manage to secure production for the class and they were withdrawn in the 1980s .
Simplified: The class was intended to be a modern DEMU to replace the ageing types in use on the Southern Region of British Railways but the prototypes built did not manage to secure production for the class and they were withdrawn in the 1980s .