Was he in command at Waterloo? (13)
I believe the answer is:
stationmaster
'was he in command at waterloo?' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'was he in command' is the wordplay.
'was he in' becomes 'station' (I can't justify this - if you can you should give a lot more credence to this answer).
'command' becomes 'master' (mastering is a kind of commanding).
'station'+'master'='STATIONMASTER'
Can you help me to learn more?
(Other definitions for stationmaster that I've seen before include "Railway employee" , "Railway official" .)