American soldier's way of working gadget (5)
I believe the answer is:
gismo
'gadget' is the definition.
(I know that gadget can be written as gismo)
'american soldier's way of working' is the wordplay.
'american soldier's' becomes 'GI's' (informal term for a US soldier).
'way of working' becomes 'mo' (abbreviation for modus operandi).
'gis'+'mo'='GISMO'
(Other definitions for gismo that I've seen before include "Device of American" , "Thingumajig - gadget" , "Useful gadget" , "Gadget (colloq.)" , "mechanical device?" .)