?As near as I can determine, Army Service Command I (ASCOM I) was constituted in the Army of the United States (AUS) and organized on Okinawa about June 1945, reporting directly to U. S. Army Forces, Pacific (USARPAC). As the desigation suggests, the command consisted of service and support troops and its principal mission was to stage supplies and materiel for the proposed invasion of Japan.
ASCOM I was redesignated Army Okinawa Base Command I (ABSCOM I) either shortly before or shortly after Japan capitulated.
You need to provide more information. 25th Infantry Division engineers was 65th Enigineer (Combat) Battalion. It's unlikely they'd have been withdrawn, even temporaily, for such an assignment - not impossible, just unlikely.
Most likely, engineers assigned or attached to ASCOM I would have been Construction- or even General Service Engineers. See if you can come up with a designation.