One with US military service, fine East African native (7)
I believe the answer is:
giraffe
'african native' is the definition.
(animal native to Africa)
'one with us military service fine east' is the wordplay.
'one with' means one lot of letters go next to another.
'us military' becomes 'GI' (e.g. 'a GI helmet').
'service' becomes 'RAF' (Royal Air Force).
'fine' becomes 'f' (abbreviation in pencil classifications).
'east' becomes 'e' (abbreviation).
'gi' put next to 'raf' is 'giraf'.
'giraf'+'f'+'e'='GIRAFFE'
(Other definitions for giraffe that I've seen before include "A long-legged creature" , "The tallest animal with long neck" , "Tallest beast" , "Long-necked animal" , "The largest ruminant" .)