Re: Search for Army Unit
Ed, as a hobbyist and casual observer, a couple of things about your post piqued my interest.
An engineer battalion and a cannon company are quite different types of units, to the best of my knowledge. A cannon company was a heavy weapons (howitzer) outfit that was customarily a part of an infantry regiment. "290th Cannon Co." would suggest to me the cannon company in 290th Infantry, one of the infantry regiments in the 75th Infantry Division.
Also, my WWII reference does not list a 355th Engineer Battalion. It does, however, list a 355th Engineer General Service Regiment which served in ETO.
Don't know if these observations will be of help, or if they will only serve to muddy the waters, so to speak. Hope it is the former.
If you could expand on the unit info you have, somehow, perhaps we could research further and help point you in the right direction.