Nicholas B Van Bergen is listed as "bur nav" on page 104 of the January 1938 Registers of the Commissioned, Warrant, and Volunteer Officers of the Navy and Marine Corps of the United States:
What does "bur nav" mean?
The US Department of the Navy (which is NOT the United States Navy) provides a governmental organisational structure to oversee the Navy.
By 1938 it was structured to include a number of "Bureaus" including the Bureau of Navigation (Bur. Nav.) which had responsibility for Navy personnel, the Hydrographic Office and the Naval Observatory. In 1942 the Bureau of Navigation became the Bureau of Naval Personnel (BuPers) and the other functions were transferred to the Office of the Chief of Naval Operations.