I am a consultant to DTRA and a retired USAF weapons maintenance officer. In researching the early histories of the Armed Forces Special Weapons Project, I found some information that adds to your history of early Navy SWUs.

The Naval Administrative Unit, Sandia Base, was established on 14 Jul 47, to provide administrative and logistical support to Navy personnel assigned to Sandia Base.

Unit "D" (Provisional) of the 38th Engineer Battalion, Special, was activated on 1 Sep 48. The unit consisted of the first Navy assembly team graduated from the AFSWP Technical Training Division (on 19 Jul 48); 13 officers, 9 warrant officers, and 16 enlisted men.  On 13 Oct 48, in accordance with a letter from the Secretary of the Navy, Unit "D" was redesignated "US Navy Special Weapons Unit No. 471". [First History of AFSWP, Vol. I - 1947-1948, Chapter 5 - Sandia Base]

FYI - the 38th was stationed at Sandia Base, NM, with the mission of "assembling and monitoring the bomb".