Complex sentence: Commissioned officers will and do perform physical labor when operationally required to do so, e.g. in combat, however it would be very unusual for an officer to perform physical labor in garrison, at home station or in homeport.
Split into simpler sentences: Commissioned officers will and do perform physical labor when operationally required to do so, e.g. in combat. However, it would be very unusual for an officer to perform physical labor in garrison, at home station or in homeport.