1000 trapped in a remarkable battle (5)
I believe the answer is:
somme
'battle' is the definition.
(Battle of the Somme in WW1)
'1000 trapped in a remarkable' is the wordplay.
'1000' becomes 'M' (roman numeral).
'trapped in' is an insertion indicator.
'a remarkable' becomes 'some' (that's some car you've got!).
'm' put within 'some' is 'SOMME'.
(Other definitions for somme that I've seen before include "Scene of World War One battles" , "French river at Amiens" , "River of northern France" , "WWI battle site" , "First World War battlefield" .)