There was one obvious clue on the photo: 3rd Anti-Aircraft Battery (C.A.C.) Even though we had a major clue, we still weren't coming up with much information. Thus, the picture was posted on the closed Facebook group: Genealogy, Just Ask for additional help.
In the meantime, it was determined that the C.A.C. stood for Coast Artillery Corps. This led to the site: Defeating the Hun: History of the United States Army Coast Artillery Corps During World War One. The author, Joe Hartwell, has compiled a wealth of information on this Ancestry Freepage. The downside, was the lack of any information about this particular unit: 3rd Anti-Aircraft Battery. After an email to the author, we were able to visit with him about this unit. Unfortunately, Joe didn't have any information on this particular unit and believed they were never deployed overseas. He said they likely came from all over the United States and that a muster roll probably did not exist.
A second site was found with information about the Coastal Artillery Corps on the World War I Vets site.
Facebook Genealogists also came thru with more information about the picture:
Thanks to everyone who helped identify the group in the picture!
We would still love to know who is in the picture!