Welcome to the forum. Wow, you've had quite a journey so far, relocating his uniforms, etc. Glad you were able to solve some of the mystery so far.
An engineer group/regiment/company, often were attached to various other units during the war. For instance, my dad (the 540th Engineer Regiment), were at times attached to (or in support of) the 82nd Airborne and the 36th Infantry Regiment, just to name a few. They went where they were needed. They served under either a Corps or an Army, such as the 5th Army, the 7th Army, or VI Corps. This was very common for "bastard" units, meaning they fought independently. Let me explain further... There were engineer units such as the 10th Engineer Regiment, who were a permanent part of the 3rd Infantry Division. They fought as a whole. Units such as your grandfather's were independent and not part of a division, thus they could be attached where needed.
Of course when you receive the history of the unit from Maryland, then this will become self-evident.
Hope that helps a bit. :blink:
Proud Daughter of Walter (Monday) Poniedzialek
540th Engineer Combat Regiment, 2833rd Bn, H&S Co, 4th Platoon
There's "No Bridge Too Far"