### Clue: Drove Mustang, say, when Ford finally replaced Sierra (5)
### Answer: HORDE 
 ### Explanation: Definition: Drove
definition: "Drove" as a noun referring to a large crowd 
a mustang is a HOR-S-E, with the final letter of [For]-D replacing S (Sierra, NATO alphabet)
 
in the surface, the Ford Mustang and the Ford Sierra are cars