Performance of US serviceman, good (3)
I believe the answer is:
gig
'performance' is the definition.
(I've seen this in other clues)
'us serviceman good' is the wordplay.
'us serviceman' becomes 'GI' (informal term for a US soldier).
'good' becomes 'g' (abbreviation).
'gi'+'g'='GIG'
'of' is the link.
(Other definitions for gig that I've seen before include "One-night stand" , "One-horse carriage" , "A one-night entertainment" , "Live musical performance" , "Live performance; light two-wheeled carriage" .)