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~ C. Plath Pedigree ~

Presented is our second opportunity in the last few months to offer an outstanding, near “Collector Quality” U.S. Navy MK III sextant. This one is Serial No. 1771 and was made by Scientific Instruments of Milwaukee, WI, the Navy’s last sextant contractor thus becoming a part of celestial navigation history. The sextant comes complete with a sighting ring, brush, an adjustment wrench and a spare index mirror, all housed in a Butternut wood case with wood handle which adds an elegant touch. The matching certificate is dated 7/10/85.

SOME BACKGROUND: At the time the design of this sextant was adopted around 1975, I was a member of the Navy Department’s Navigation Symposium Board, and remember the criteria that was established for as new sextant design which was the same as the already existing features found in sextants in the civilian maritime industry. The Navy’s design incorporating these features was late in coming since the civilian sextants were in use before WW II and were far advanced from the ubiquitous Navy’s standby during this period, the Navy MK II.

Listed are the MK III’s design features:

  • Light weight
  • Large size index mirror
  • Large size horizon mirror
  • Lighting system
  • Vernier reading to 6 seconds
  • Handle for ergonomic fit
  • Wide angle telescope
  • Non adjustable instrument error of less than 20 arc seconds
  • Military high impact absorbent case

Except for the handle and case, the Tamaya MS 733 and the C. Plath sextants met these criteria as did a few others, but there was strong feelings in government to “Buy American” in contrast to today’s World Economy. Consequently, M. Low of New York City was selected for the MK III program, Little is known of this company other than they were in New York and in the instrument business. The sextants were made under license from C. Plath, of Hamburg, Germany who may have provided the tooling. C. Plath aficionados take note, the design is clearly the same as the C. Plath Classic sextant down to the last detail other than its ergonomic handle and large size high impact resistant case. This pedigree is noted on page 119 of the book by Friedrich Jerchow,“From Sextant to Satellite Navigation, (1837-1987) 150 years C. Plath”.

After M. Low disappeared from the scene, Scientific Instruments, of Milwaukee, WI. became the sole provider, but they made fewer and fewer sextants as Satellite Navigation (Sat Nav), the newly accepted electronic system, became more prevalent until GPS succeeded it. SIC stayed in business until 2008 when they decided to close their doors. In one of our last conversations with the owners they told us sextants were still being made in very small numbers for newly built U.S. Navy ships at a price of $4300.00.

CONDITION: The sextant shows light evidence of service of sea, but not much. The interior of the case is in the best shape that we have seen, and there are no wounds from the sextant’s legs missing their holes that were prevalent
in the others we’ve seen. All its machinery works well. Both fitted mirrors show as NEW. The stainless screws and clamps are bright and shiny, but there is some minor roughness to the black finish. Even so, it can be considered as near new in all respects. It comes with an extra index mirror. The numbers match on the certificate. The lighting works. The newly refinished Butternut case shows some minor scars of age such as a few scratches on its top and bottom. The index error is negligible, and there is a touch of side error which is a good thing. The last certificate is included. No locks are fitted to this Navy style case.

STAR RANKING: This sextant and case rates 5 STARS

Flawless index mirror Perfect horizon mirror
Vernier with 10 indents or each 6″ Maker’s tag
Large Butternut wood case with hi-impact interior

This is fine sextant is in perfect condition and is backed by our guarantee of satisfaction. It requires someone who can appreciate the fine points of a sextant, and is willing to pay an appropriate price for this level of quality and excellence.

OUR QUALIFICATIONS: We are one of the few company’s still selling navigation
instruments that know anything about them. For purposes of judging whether Joel’s opinion counts, he was the editor of the chapter on sextants of the 1977 Edition of “Bowditch”, The American Practical Navigator, NAVPUB 9; a member of the U.S. Naval Academy Navigation Symposium Board, 1975 -1978; the author of a book on marine sextants, Cornell Maritime Press,1975, and the founding president of Nautech Maritime Corporation which partnered with Tamaya of Japan in the introduction of their sextants and the famous NC-2 navigation computer, in the U.S. market. Joel is also a retired Master Upon Oceans, and held a U.S. Navy “D” Qualification as a Senior Skipper – Oceans. From 1995 through 2000, he served as a Varsity Offshore Sailing Team coach at the U.S. Naval Academy.



Measuring Range: -5 to 125 degrees
Accuracy: Tested to +/- 20 arc seconds
Telescope: 2 x 40 Coated optics
Frame: Aluminum with black enamel paint and white numbers.
Micrometer Drum and Vernier Scale: reads to 6 arc seconds
Index Mirror: 57 x 42 mm with spare
Horizon Mirror: 57mm diameter with spare
3 for index mirror
3 for horizon mirror
Illumination: Yes

Weight sextant: 2.5 lbs, Weight case in case 12.5 lb


1 Sextant frame
1 2 x 40 Scope
1 Mirror adjustment tool
1 Spare index mirror
1 Brush
1 Bulb
1 Mahogany sextant case. No locks
1 Certificate dated 1985


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Shipping & Packaging

The cost of shipping, packing, handling, and insurance to your destination, will be calculated point to point and is an additional charge. You may email us to get these costs. We price our shipping honestly, but we expect to be reimbursed for the nominal cost of packaging materials and handling.

Our Unconditional 'No Nonsense' Guarantee

If not completely satisfied with your purchase it may be returned, if without damage, within three days of receipt in its original packaging. Return items must be insured for their full value. Only a prior email authorization by us for the return is required. Shipping charges are refundable if due to our error within the continental United States.

International buyers welcome, but inquire first. We have satisfied customers worldwide.

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Established in 2003

Celebrating 18 Years of Exellence in Nautical Antiques

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