Faking it. Is it a SNO-M or is it a C Plath?

14 07 2010

In my post for October 2008, I wrote about the USSR SNO-M sextant and gave my opinion that it was identical to the alumium alloy-framed C Plath sextant of WW II. This was based on examination of photographs of putative WW II Plath sextants sold on e-bay, complete with Nazi insignias and Kriegsmarine index numbers. Serial numbers placed them in 1942 and 1943 and their frames were identical to the much later SNO-M frames, with the same pattern of sprues and risers from the casting process visible on the back of the frames (Figure 1). I strongly suspect that these so-called C Plath sextants are forgeries based on changing the obviously different SNO-M index arm and engraving C Plath logos and numbers on to the ends of the limb, which are conveniently vacant for them.

Fig 1

Now it could be argued that the differences are because the backs of the frames were not finish machined because of pressures of war time production. This will not do, as there are other, more subtle differences, indicated in Figures 1 and 2, which show that even allowing for the traces of the casting process, different dies were used. The dies used for pressure casting are very expensive to make but when casting aluminium could be expected to last for up to 100,000 units. During WW II, C Plath made about 11,000 nautical sextants, so it is not very likely that duplicate dies were made or that the original die set wore out. Furthermore, I have been able to examine an indisputably C Plath sextant, whose serial number falls between those of the two probable fakes, differing by only 289 from one of them. Its frame is not the same. (April 2013) Since writing this in July, 2010, I have had the opportunity of examining an indisputably genuine Kriegsmarine sextant from late 1944. The rear of the frame had not been fully machined but other features of the frame casting were as for earlier, genuine, sextants. The official history of C Plath writes of labour shortages at this time.

Fig 2

But it is not just in the frame that there are differences. Cast into the interior of the mirror brackets are part numbers preceded by the initials “C. P.” (Figure 3), while no such numbers will be found inside SNO-M brackets; and the foot of the horizon mirror bracket is displaced upwards in the SNO-M Figure 4). Again, it will not do to argue that extra sets of dies existed, and even if they did, it is difficult to think of a reason why the horizon bracket might have been modified in the middle of a war that was slowly being lost.

Figure 3

Fig 4

The index shades seem to be identical, except that the little brass knobs have a traditional shape in the Plath and are stark cylinders in the SNO-M. Again the horizon shades seem identical, but their mounting s are not. I have circled two points of difference in Figure 5

Fig 5

The index arm of the C Plath sextant was made in two parts, joined by four screws just above the lower index arm expansion, while that of the SNO-M, which carries the serial number, is a one piece alumium stamping with an integral stiffening rib. Obviously, this must be replaced in a forgery and insignia applied(Figure 5), but there is a more subtle difference. To make the arm in two pieces requires that the upper part must be displaced downwards by the thickness of the metal. Careful examination of the upper end of the index arm will show that in the SNO-M (and the probable fakes) is sandwiched between the index mirror bracket and the disc to which the bearing shaft is attached. In the Plath instrument it is the disc that is sandwiched between the bracket and the index arm (Figure 6).

Fig 6

Fig 7

The limb and the rack of the Plath sextant are both of the same radius, while in the SNO-M, the edge of the limb has been machined away and its radius is about 1 mm less (Figure 7). This is also true of the re-incarnated “Plaths” which also all seem, like the SNO-M, to be quintants reading to 140 degrees . The genuine drum is divided to half minutes, unlike the SNO-M, which is divided only to single minutes.

Fig 8

The handle is less easy to fake. The genuine wartime Plath has the Plath logo and name moulded into it (Figure 8), whereas the SNO-M has a brass-lined hole by which it is retained in its case by means of  a spring latch. Telescopes too are difficult to replicate (though Tamaya may have done so during WW II) and I have found no evidence to suggest that Plath varied the form of the standard star telescope (Figure 9) until after WW II.

Fig 9

Fig 10

Figure 10 shows that  the famous C Plath stick man logo has feet that are too big, has bursitis in the right elbow and shows detail of the index mirror that is not visible in the genuine contemporary logo. The genuine instrument also has the letters “D. S.” stamped next to the logo, showing that it had been examined at Deutches Seewarte, the German Naval Observatory in Hamburg.

Fig 11

Finally, many of the features of the genuine article (as opposed to a re-worked SNO-M, may be seen in Figure 12, which is from the front cover of Die Woche (The Week) from April 1943.

Fig 12




10 responses

4 01 2012
Greg Smith

Nice work on this blog, with respect to your “case” observation. I have in my posession a late WWII C Plath sextant “M20984” I was left to me by my great uncle, he served as a senior officer in the British merchant marine during WWII. The back of my sextant has all of the “riser” issues and the lack of a smooth back like a “fake” SNO-M, but has the correct arm, correct countsinking for index shades, correct 120 degree radius, correct filter knobs, correct base on the filters, correct base on the horizon mirror, correct marks inside the mirror housings, and correct telescope.

Interestingly The adjustment on my horizon mirror is different than the one your picture. It does have the “center foot” but the adjustment on the top is horizontal not vertical like the Plath one.

My Sextant also has a HUSUN calibration card that declares it a Plath that is dated August 1947. Which of course is after WWII. I wonder if these were sold as surplus after the war or were converted for civilan use post war. The Nazi markings are there but they have been “shoe polished” over. The Plath logo in the handle has been machined out.

It has been in my family since the late 40’s, maybe earlier.

Would love to know more about this interesting device.

4 01 2012

Thank you for the comments, Greg. If it walks like a duck, looks like a duck and quacks like a duck…
Forgeries tend to fail on the details and in your instrument most of the details seem to be correct. It may be that under the pressures of a war time economy, Plath didn’t bother to machine the backs of the frame, though in my instrument, made in 1943, about a year after yours, the finish is very good. I think in view of its provenenance, one has to accept your sextant as genuine.

It may be that your instrument was among the spoils of war. As it was plainly in Britain by August 1948, it cannot have been part of war reparations, as C Plath’s machinery was not confiscated until early in November of 1948. Interestingly, the only machine that was not confiscated was the dividing machine, which had been dismantled and hidden immediately after the war ended in 1945.


4 01 2012


You note that your Plath is a 1943 and is newer than mine. I take it that is based on the serial number. Is there a data base of Plath Serial numbers somewhere? Can you decode the actual year of manufacture from the serial number? or even better which ship or officer used it?

If it helps with your research I would be happy to send pictures of my sextant curiosity. As I noted, sometime early in its life, much of the “Hamburg” and other German markings have been machined off of my Sextant, which I can only suspect completely devastates any collectable value. I can only imagine that in 1947 the British and Canadian’s were still a little “cool” to all things German.

4 01 2012

I and a friend have compiled a data base of serial numbers linked to the date of the inspection certificate, which of course is not necessarily the date of manufacture. It is not in a form suitable for posting on the blog, but I would be happy to send a copy to you (and anyone else) if you use the “Contact me” tab on the home page (rather than as a “Comment”) or direct to engineer@clear.net.nz. C Plath may still have the original books. I would be happy to see pictures of your instrument and with your permission add one or two to the blog post if appropriate. While the Nazi era markings add value to the instrument for a certain type of collector, your sextant still had monetary value, but in view of its provenance, you would probably not want to sell it anyway.


10 01 2012


I have one more question about my sextant. I noticed on the spreadsheet you sent (thank you by the way) You have in some cases a serial number and a Navy/Ship/Boat Number. I gather that the serial number is the number on the frame near the radius at the right hand end (“0” end) of the scale and the Navy Number is on the Arm, under the “M”.

Any indication what the Navy number means? Or what it was used for?

Thanks again, you have been an awesome resource.


10 01 2012

Yes, Greg, The number at the zero end of the limb is Plath’s serial number. I don’t know exactly what the naval number indicates, but assume it is the unique identifier for naval stores purposes. Googling “Kriegsmarine” may help – and will certainly keep you occipied for many hours.

17 11 2013
Tim Bradbrooke

Bill and Greg,
I find this process of comparison between fake and genuine quite fascinating. My father just passed away and I found a C Plath Sextant among his effects. He was in the RAF in WWII and later worked for Hoechst Chemical AG based in Frankfurt (formerly part of I.G. Farben, makers of the infamous “gas”). Mine matches all the important “details” as does Greg’s. Also, like Greg’s, mine was only partially machined on the back, and does have risers from the casting process. These riser locations differ from the Russian SNO riser locations. I wonder if my riser locations are the same as Greg’s?
For instance, in your “Fig 1” where you identify a “riser”, there is no such riser on mine. My holes that are “wider apart and differing in location” from the SNO versions have a “riser” at the lowest point of the frame, below the lowest hole. There is not enough room for such a riser in the SNO version because of the differing hole locations, so they appear to have put their riser between these two holes. My bet is that Greg’s risers are similarly located (a good way to distinguish real from fake?). In “Fig 2” my riser is not between the two holes as in the SNO version, but is half an inch to the right. Further, there is no riser on the end of the limb despite being unfinished. My handle has also been machined to eliminate the logo like Greg’s. Similarly, there is no stickman or D.S. on the end of the limb (despite it ending in 120, rather than 140). It does not appear to have been machined off, just never engraved to begin with… My serial number is 26791 with a card dated Jan 6, 1945. The naval designation below the M is 11041. The drum is in half degrees, and there are C.P. numbers under the mirrors (R-616-7.02-18). The handle also has some symbols underneath (IRS; 9366 with an oval around it, as well as another stamp I can’t read). It looks like there were indeed labor issues towards the end of the war, and cosmetic stamping and logos may have been skipped. What is your opinion? Also, how much are these sextants worth?
Thanks, Tim

17 11 2013

Thank you Tim, for your comments. This post has attracted more comment than most.

I now accept that as WWII progressed, finish suffered and the back of the sextant was not machined flat. According to Jerchow’s history of C Plath (From Sxtant to Satellite Navigation, Hamburg, 1987), when Hamburg came under bombing attack some production of sextants and other bearing devices was moved to a satellite factory in Scharfenwiese with production beginning in January 1944. As the eastern front moved nearer, the factory was moved to Guttstadt towards the end of 1944 and then abandoned. It is possible that the sextants with points of difference were produced in this satellite factory.

At least one smaller British firm of instrument makers produced hybrid sextants from surplus or scavenged parts, some of them recognisably by Plath, in the early 1950’s. I wonder whether whole sextants may have lost their identities…

19 11 2013
Tim Bradbrooke

Guttstadt would seem to match the Jan 5, 1945 date on my card. Does my high serial number indicate such a date as well?
Greg said that the logo on his handle seemed to have been machined out. Mine appears that way as well. However, it has just occurred to me that the machined recess might be there to accept a disc with the C. Plath logo on it. Is the logo made of a different material? Do they appear to have been pressed into the plastic handle? Also, the fact that Guttstadt was so late in the game might explain why they weren’t inspected by D.S. hence the absence of stick figure and D.S. stamps. Does this rarity help the value, or does the absence of stamps outweigh this?
Regarding the finishing on the back, I find it interesting that mine is partially finished on the back. Why stop halfway? Was the worker interrupted by something? One can just imagine…
Thanks, Tim

19 11 2013

The logo is moulded into the handle, Tim. The serial number fits with the late date. I can’t really comment about the effect on value as I am not a dealer, but I would be inclined to pay less for it if a collector and no change if I simply wanted a good sextant to use. One class of collector goes for the Kriegsmarine stamp on the index arm, though some nations, like the Netherlands, find all depictions of the swastika offensive and illegal.

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