Arm with US bombs and first-class fighters (7)
I believe the answer is:
samurai
'fighters' is the definition.
(swordsmen in feudal Japan)
'arm with us bombs and first-class' is the wordplay.
'with' means one lot of letters go next to another.
'bombs' indicates anagramming the letters.
'and' means one lot of letters go next to another.
'first class' becomes 'ai' (A1 - top quality).
'arm' put after 'us' is 'usarm'.
'usarm' with letters rearranged gives 'samur'.
'samur'+'ai'='SAMURAI'
(Other definitions for samurai that I've seen before include "Sudoku variant" , "Traditional warriors of Japan" , "military man" , "Member of Japanese warrior caste" , "Seven -, film directed by Kurosawa" .)