I have found a few sites that might give some information.
At least two are about veterans from the 603rd Engineer Camouflage Battalion or the 23rd Headquarters Special Troops.
The next few are some secrets about that group, pictures, or a few operations.
The box number in the Archives is Box 664 for the 603rd Engineer Camouflage Battalion.
The last website is source that you can use to find information on the group. However, it will need a name from a person in that group. It is similar to ancestry. However, is very useful and organized.
Dear Mr. Moran,
Thank you for posting your request on History Hub!
We searched the World War II Operations Reports, 1940-1948 in the Records of the Adjutant General's Office, 1905-1981 (Record Group 407) and located General Orders for 1944-1945 and Operation Reports for 1 July - 9 November 1944 of the 603rd Engineer Camouflage Battalion. We also located an Official History for July 1944 - March 1945 of 23rd Headquarters Special Troops. There are additional records of the 23rd but they are listed by the name of the various operations it participated in.
For access to and/or copies of these records, please contact the National Archives at College Park - Textual Reference (RDT2) via email at firstname.lastname@example.org.
We hope this is helpful. Best of luck with your research!