The only reference i found for to the 393rd Eng GS Reg. was found here:
Historic Context for the African American Military Experience: Section 9, Part III
393rd Engineer General Service Regiment- Activated at Camp Clairborne, Louisiana, and returned after a short stay at Camp Robinson. Staged at Camp Patrick Henry, Virginia.
The 38th Engineer General Service Regiment is listed as a non-divisional unit for the Normandy invasion.
38th Eng Reg WWII Timeline
1 October l933 organized as the 38th Engineers (General Service) Regiment.
13 January 1941 the 38th Engineers (General Service) Regiment was re-designated as the
38th Engineers (Combat) Regiment.
28 May 1941 activated as such at Fort Jackson, South Carolina. Participated in the
Carolina Maneuvers, September - November 1941.
14 March 1942 departed Charleston, South Carolina.
30 March 1942 arrived on Ascension Island and began construction of an airfield.
19 August 1942 departed Ascension Island.
23 August 1942 landed at Pointe Norie, West Africa.
30 December 1942 first increment moved to Dakar, Africa
17 February 1943 second increment moved to Dakar, Africa
29 May 1943 the 38th Engineers (Combat) Regiment was re-designated as the 38th Engineer Combat Regiment.
8 December 1943 departed Africa.
1 January 1944 the 38th Engineer (Combat) Regiment was re-designated as the
38th Engineer General Service Regiment.
4 January 1944 arrived in England
9 June 1944 landed in France and was assigned to the Normandy Base Section.
13 March 1946 arrived New York.
14 March 1946 deactivated at Camp Kilmer, New Jersey.