This is a rugged, reliable, and ergonomic multi-shot bubble sextant with a
median device that was developed for the U.S. Army Air Corps for use in World War II. By 1942 Link was building hundreds of these sextants each week, at a unit cost of $262. Theodore "Dutch" Van Kirk, the navigator of the Enola Gay, used an A-12 on the long flight across the Pacific and back in August 1945. A month later the A-12 was considered war-surplus, and available at deeply discounted prices.
Ref: Link Bubble Sextant (Octant) Model A-12 Handbook: Description,
Operation, Use, Adjustment (Binghamton, N.Y.: Link Aviation Devices, Inc., 1943).
U.S. Air Force, Air Navigation (1951), p. 263.
Gunne Lowkrantz and Edwin A. Link, Jr., "Recording Navigation
Instrument," U.S. patent #2,349,506
Edwin A. Link, Jr. and Harold A Marsh, "Navigation Instrument," U.S. patent #2,359,484
H. A. Marsh, "Case for an Octant or the Like," U.S. design patent D132,977