I'm back. The 1280th was NOT under a division. Units such as his (and like my father's), were "bastard" units and served under an ARMY or CORPS. These units were placed where needed and often were attached to other units, such as infantry, as temporary measures. This was something I learned years ago, when I first began exploring my father's history. I was very familiar with the layout of armies, but had no idea at that time, that independent engineer units, even existed.
Infantry units had their own (organic) engineer battalions. The 65th Infantry's engineers would have been the 265th Engineer Combat Battalion, not your father's unit.
For instance, when the 540th landed on the beaches of southern France, my father's engineer regiment was under the jurisdiction of VI Corps/7th Army. When they were in Italy, it was the 5th Army.
Proud Daughter of Walter (Monday) Poniedzialek
540th Engineer Combat Regiment, 2833rd Bn, H&S Co, 4th Platoon
There's "No Bridge Too Far"