65th Service Squadron / 65th Service Gp

I'm trying to find anything on my grandfather's service in WWII.  I have his discharge certificate that says his organization was 65th Service Squadron / 65th Service Gp.  His place of entry was "Rctg Sta Barksdale Field La" in 1940.  His occupational specialty was AP Instrument Mechanic 686 and occupation was Marksman Carbine.  I also know he was a medic/first aid man.  The Battles and Campaigns are "Northern Solomons and New Guinea GO 33 WD 45".  How can I get anything more specific?  I wish I would have asked more questions growing up.  Please let me know where I need to start.

I think Mark is right in narrowing this to the 65th Service Sq, based on the campaigns your grandfather participated in.  This unit was constituted 20 Nov 1940 as the Materiel Sq, 50th Air Base Gp and activated 15 Jan 1941 at Maxwell Fld, AL.  Two days later, it was redesignated the 65th Materiel Sq (still assigned to the 50th Air Base Gp -- later 50th Service Gp).  In August 1941 it moved to Harding Fld, LA.  I do not have the exact dates in 1942 on which it moved to Australia and the Southwest Pacific.  For a time it was attached to Task Force 6814 (later the Americal Division).  It was redesignated 65th Service Squadron in 1942 (September?) stationed at Noumea, New Caledonia (now Vunatu) prior to Apr 1944, but I do not have exact dates.  It was redesignated the 65th Air Service Sq on 31 Dec 1943 (I believe the source for this date may be in error and the redesignation was on 31 Dec 1944).  In the Philippines, it was also stationed at Zamboanga after redesignation as the 65th Air Engineering Sq, and was reassigned to the 29th Air Service Gp.  It moved to Japan as part of the occupation force and was stationed at Yokota AB until Aug 1948 when it was inactivated, then disbanded on 8 Oct 1948.