Medicine served up in prison, one in disastrous campaign (9)
I believe the answer is:
gallipoli
'campaign' is the definition.
(I've seen this before)
'medicine served up in prison one in disastrous' is the wordplay.
I cannot really see how this works, but
'one' could be 'li' (I've seen this in other clues) and 'li' is found in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for gallipoli that I've seen before include "Long ago landing" , "military campaign" , "Scene of WW2 landing in 1915" , "Turkish site of WW1 campaign" , "World War I battle of the Dardanelles" .)