A musical pair of American soldiers (4)
I believe the answer is:
gigi
'a musical' is the definition.
(1973 musical)
'pair of american soldiers' is the wordplay.
'pair' says to double the letters.
'of american soldiers' becomes 'GI' (e.g. 'a GI helmet').
'gi' doubled is 'GIGI'.
(Other definitions for gigi that I've seen before include "Musical, winner of nine Academy Awards" , "1958 film, winner of 9 Academy Awards" , "musical from the 1950s" , "Play" , "Lerner/Loewe musical" .)