The Navy Mark II sextant by David White Company of Milwaukee was one of the principal instruments of U.S. Navy navigation throughout World War II. This example, serial number 647-1939, was inspected and certified by the U.S. Naval Observatory in Washington on August 15, 1941 — just four months before Pearl Harbor — making it a genuine pre-war/early-war service instrument. The limb reads to single degrees with drum micrometer to 1 minute, and vernier to 6 seconds of arc. Original mahogany dovetailed case with brass hardware and David White Company nameplate. Original inspection certificate with handwritten eccentricity corrections and inspector’s signature survives intact. Telescope present.