I can't get my WWII reference book (which is highly regarded) to correlate with the info you had in your inquiry. According to my reference:
There were three field artillery units with the "8th" designation in WWII: 8th Field Artillery Regiment, 8th Field Artillery Battalion, and 8th Field Artillery Observation Battalion.
The 8th FA Observation Battalion was never in Hawaii.
The 8th Field Artillery Regiment, stationed in Hawaii, was redesignated the 8th Field Artillery Battalion in October, 1941. It says further that they received campaign credit for Central Pacific, Guadalcanal, and Luzon. It does not indicate they were ever in the European Theater.
Are you sure the unit about whom you are seeking info served in ETO?
The "5th Infantry" would refer to the 5th Infantry Regiment, which was one of the rifle regiments in the 71st Infantry Division. This unit, and the 5th Infantry Division, served in the European Theater. However, the closest thing either has to an "8th" in their artillery units is the 608th FA Battalion in the 71st ID.
Could it be the unit about whom you are seeking info served in the Pacific Theater with the 25th Infantry Division? It appears to me that the 8th Field Artillery Battalion did so. More info in that regard can be found at this web page: http://www.25thida.org/units2.html#FArtilleryhttp://www.25thida.org/units2.html#FArtillery
I hope this is helpful. If I have missed something, or if there is something further we can pursue, don't hesitate to post.