A bridge may be built by this military unit (7)
I believe the answer is:
brigade
'this military unit' is the definition.
(brigade is a kind of military unit)
'a bridge may be' is the wordplay.
'may be' is an anagram indicator.
'a'+'bridge'='abridge'
'abridge' anagrammed gives 'BRIGADE'.
'built by' acts as a link.
(Other definitions for brigade that I've seen before include "Abridge (anag)" , "Army subdivision" , "Set of troops" , "Corps" , "Company" .)