Soldiers behave like troopers in jacket and tie? (8)
I believe the answer is:
menswear
'jacket and tie?' is the definition.
(jackets and ties are examples of menswear)
'soldiers behave like troopers' is the wordplay.
'soldiers' becomes 'men' (men can mean a group of soldiers).
'behave like troopers' becomes 'swear' (as in 'swearing like a trooper').
'men'+'swear'='MENSWEAR'
'in' acts as a link.
(Other definitions for menswear that I've seen before include "Boxers, for example" , "Sort of clothing" , "Traditionally suits, shirts etc." , "Suits, trousers etc" , "Male clothing" .)