Civil War fortification diagram

The note on your file is a citation for the record location, but I think it should read as "RG77" (record Group 77, Corps of Engineers).  You have a box number, but no series or entry number.  I could be wrong, but I surmise it is in Entry 161 (Field Survey Records).

The Nat'l Archives probably won't supply an image unless it is already in their catalog.  I don't think it has been digitized yet.  The entry in the on-line catalog is at this link : https://catalog.archives.gov/id/597209

Dear Mr. Brockenbrough,

Thank you for sharing your question with the History Hub.

As Mr. Deiss indicated, it is possible that the diagram you are interested in is part of the series Field Survey Records, 1794-1916 from National Archives Record Group 77: Records of the Office of the Chief of Engineers (OCE). These records are in the custody of the Textual Reference Branch at the National Archives in Washington, DC (Archives I). You can contact them directly at archives1reference@nara.gov with questions about the records and about ordering reproductions.

It is also possible that the diagram is part of the series Civil Works Map File (also from RG 77), which is in the custody of the Cartographic and Architectural Section at the National Archives in College Park, MD (Archives II). Many of these records have been digitized, including this [Sketch of action near New Cold Harbor, Va.]. You can search within the series via the National Archives Catalog link above, and you can contact the Cartographic and Architectural Section directly at carto@nara.gov with questions about these records or about ordering reproductions.

Thank you, again, for posting your question on the History Hub, and best of luck with your search!