divisor line
~ C. Plath Pedigree ~


Presented is only the fourth Navy MK III that we have offered for sale in eight years. This one was made by M. Low, the original manufacturer of this design. It differs from those made by Scientific Instruments by having the M. Low name engraved on the index arm. Scientific Instruments of Milwaukee, WI riveted a tag on the index arm which lead us to believe SI may have acquired parts from M. Low and used that method to cover the Low name. The sextant comes complete, and fully functional with a working internal light, adjustment wrench, brush and the original inspection certificate dated March/25/70. A copy of the Navy ten page instructons are also included. The low number and the early date may indicate this instrument was made for the Navy’s evaluation.

SOME BACKGROUND: At the time the design of this sextant was formally adopted around 1975, I was a member of the Navy Department’s Navigation Symposium, and remember the criteria that was established for a new sextant. They coincided with already existing technology in the civilian maritime community. In total, the new design was far advanced from the ubiquitous Navy WW II standby, the Navy MK II which was long out-of-date.

Vernier reads to 6 arc seconds Engraved maker’s name

The Tamaya MS 733 and the C. Plath Classic sextants met the Navy’s design criteria as did a few others, but there was strong emphasis in government procurement to “Buy American” in contrast to today’s World Economy. This I found out when the sextant we submitted was praised by the ship it was used on, but our proposal was rejected. Consequently, the little known instrument maker, M. Low of New York City was originally selected, and after they went out of business, Scientific Instruments of Milwaukee, Wisconsin became the sole manufacturer until they ceased operations in 2008 as a result of the economic recession.

The fact is that all MK III sextants were made under license from C. Plath, Hamburg, Germany. 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, and this pedigree is noted on page 119 of the book by Friedrich Jerchow, “From Sextant to Satellite Navigation, (1837-1987) 150 years C. Plath”.

NAVY CELNAV TODAY: The Navy has moved away from traditional celestial navigation and even the use of paper charts. Their reliance is totally electronic position fixing. CelNav is no longer taught at the U.S. Naval Academy. Whether or not ships carry sextants today is meaningless since it is not practiced as part of the daily routine. Ten years ago I was invited to go on a brief cruise on the Spruance Class destroyer, USS CARON DD 970 as a Distinguished Visitor (DV). I used the one they had with good results (i.e. within one nautical mile of the ship’s GPS position), but no one in the wardroom or the lead quartermaster was interested in taking any sights. I appreciated its lighter than average weight, and comfortable handle.

In January 2008, Scientific Instruments ceased operations. Up to then they furnished two MK III sextants to newly commissioned ships at a price of $4300.00 each.

MK III DESIGN CRITERIA: Listed are what were “state of the art” design features, that are still the standard today:

  • 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


The sextant shows minor evidence of use which is to be expected after 42 years, but we fitted two new mirrors, replaced the missing adjustment wrench, touched-up the paint, and repaired the lighting so it works. The rest of the paint is in very good condition with no imperfections. The chromed screws and springs are all bright and shiny. All the machinery works smoothly. The original horizon mirror is still usable and acts as a spare. The old index mirror was disposed of. We refinished the Mahogany case which has some abrasions and scratches form its service at sea. The original March, 1970 certificate is included and matches the sextant’s serial number. No locks are fitted to this Navy style case. After adjustment, the index error is negligible, and there is a touch of side error which is a good thing.

STAR RANKING: This sextant and case as reconditioned rates 5 STARS

New index mirror New horizon mirror
Refinished Mahogany case with hi-impact cushion interior


This is only the fourth Navy MK III sextant we have offered in the last eight years. It will be equally at home at sea or in a collection of fine instruments. They are becoming scarce since the Navy no longer uses them.


PLATH COMPANY HISTORY: In brief, Carl Plath started manufacturing sextants, in addition to other nautical products, in Hamburg Germany in 1862 by th purchase of David Filby Company, a Hamburg instrument maker of repute, which started making sextants in 1837. As a result WW II, C.Plath was dismantled completely by the occupation forces. Around 1950, various prohibitions were lifted, and C. Plath was allowed to begin production again of sextants and other nautical instruments. Also in 1949,C.Plath was offered a gyrocompass patent and in 1951 the first gyrocompass designed to this patent was presented to the public. C.Plath progressed from the role of instrument maker to that of a modern marine navigation equipment manufacturer. In the following years the product range was expanded by many more modern designs such as autopilots, speed logs, radio direction finders, etc.


In 1962 C. Plath was acquired by Litton Industries, a large American concern. The C. Plath North American Division was set up in 1978 in College Park near Washington. 1996 saw the introduction of the world’s first fiber-optic solid-state gyrocompass by C.
Plath. The first-ever gyrocompass with no moving parts. Sperry Marine was formed in 1997 with the combination of C.Plath,
Decca Marine and Sperry Marine with more organizational changes yet to come. After 163 years, C.Plath changes its name to
Sperry Marine in May 2000. In 2001 Sperry Marine becomes part of the Northrop Grumman Corporation.

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, 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 the MS 733 Spica, the MS 833, Jupiter, MS 933 Venus sextants and the famous NC-2 navigation computer,
in the U.S. market. Joel is a retired Master Upon Oceans, and held a U.S. Navy “D” Qualification as, Senior Skipper – Oceans. From 1995 until 2001, he was a Varsity Offshore Sailing Team Coach at the U.S. Naval Academy.  Some of his present and past memberships include the: Association of Naval Aviation, Silver Wings, The Tailhook Association, McCampbell’s Aces Squadron, Naval Historical Foundation, Naval Academy Sailing Squadron, and the Naval Order of the United States.




Measuring Range: -5 to 125 degrees
Accuracy: Tested to +/- 20 arc seconds
Telescope: 4 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
Horizon Mirror: 57mm diameter
3 for index mirror
3 for horizon mirror
Illumination: Yes

Weight sextant: 3 lbs 9 1/2 oz, Weight case in case 12 lbs.


1 Sextant frame
1 4 x 40 Scope
1 Mirror adjustment tool
1 Brush
Mahogany sextant case. No locks
1 Certificate dated 1970
1 Copy of Navy’s instructions as to use

divisor line
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.

Standard Forms of Payment

Bank wire transfer, cashier’s check, money order, or personal check in which case the item will be held until cleared. Our prices are quoted net to us so that the use of credit cards or PayPal incur extra charges. Terms on overseas sales are different.

Established in 2003

Celebrating 18 Years of Exellence in Nautical Antiques

Join Our Mailing List

By submitting this form, you are consenting to receive marketing emails from: Land and Sea Collection. You can revoke your consent to receive emails at any time by using the SafeUnsubscribe® link, found at the bottom of every email. Emails are serviced by Constant Contact