This is a list of serial numbers, observed in collections and recorded from sources online, of German Kriegsmarine sextants manufactured by Carl Plath of Hamburg mostly from 1939 to 1945, marked U.D.F. — Unterseebootdoppelfernrohr (U-boat surface targeting binoculars) — equipment of the Unterseebootwaffe (U-boat Service, Submarine Service) of the German Kriegsmarine (Navy) during World War II.
Die Woche (The Week) – Berlin – April 14, 1943
In 1862, Carl Christian Plath purchased a small established German navigation
instrument store founded by David Filby, a professional precision instrument maker, 25 years earlier. This company checked and certified sextants, barometers and compasses aboard ships in North Germany and also hand-built these instruments one by one.
Plath broadened the base of the former Filby business. In 1865, Plath purchased a circular dividing machine for engraving the
graduations on the arcs of the sextants he was producing.
Soon Plath was manufacturing a broad line of nautical instruments, including compasses of all sorts, his newly patented lightweight compass card, patent logs, sextants and octants. In 1889, at the Hamburg Crafts and Industry Exhibition, Plath received high praise and a Gold
Medal for excellent precision work and the best made instruments in Hamburg.
In 1899, Carl Plath’s son, Theodor, became a partner in the family business. At this time, it was no longer efficient to produce sextants with the old circular dividing machine which Carl had purchased in 1865. Theodor was instrumental in developing a new electrically operated dividing machine which saved hours of manual labor and improved the accuracy of the sextants that were produced. The world renowned C. Plath sextants were manufactured on this machine until World War II.
Together, Carl and Theodor, showed and demonstrated their precision instruments at the Paris World Exhibition in the German Shipping Pavilion in 1900. The exhibition jury presented C. Plath a silver medal, conferring upon them, “the highest distinction for nautical instruments in commercial shipping.” This achievement cemented the exceptional reputation of C. Plath products throughout the world.
CARL PLATH / HAMBURG – Kriegsmarine sextant in original wooden box
The early 1900’s was a period of experimentation in aviation, and C-Plath was approached by pioneers in this field to develop a compass with a rotatable ring marked in degrees from 1 to 360 that would determine drift and the necessary correction angle. This new easy-to-read compass was the forerunner of the gridcompass C. Plath manufactures today.
In 1930, Theodor’s son in law, Johannes Boysen, began an apprenticeship to take over the leadership role of C-Plath. Boysen took the company from a specialty craft house to a full-fledged industry, taking
the company from 34 employees to 400. The company, miraculously survived World War I, the World Economic Crisis (the Great Depression in the USA), and even WWII at which time C. Plath provided state-of-the art gyrocompasses and navigation instruments to the III Reich.
At the end of WWII, the company almost disappeared when the Allied Forces dismantled the factory due to the prohibition of shipbuilding in Germany. Also, Boysen, the company president, was required to serve a two year prison sentence because he provided equipment to the German military during the war. At this time, the factory was relegated to manufacturing typewriters, spray guns and the works for station clocks of the Hamburg rapid transit system. But with the relaxing of the shipbuilding prohibition in 1949, C. Plath gradually returned to its roots and began manufacturing marine instruments again. By 1953, Boysen had worked out a relationship with Captain Weems to sell C. Plath sextants and compasses in the USA, hence the name Weems & Plath.
CARL PLATH / HAMBURG – Kriegsmarine sextant with “Sonnenschiesser” (“Sun Shooter”) logo on black Bakelit (Bakelite) handle
A reticle within the right prism, in the form of a single black vertical line in daylight or a single white vertical line at night (illuminated by luminous paint), always aligned exactly on the target bearing.
Although not much larger than the standard 7×50 Dienstglas (overall length 20 cms, 7.87 inches), U.D.F. are built of massively strong, heavy cast bronze construction, and weigh approximately 6 kgs (13.23 lbs). Designed to resist the crushing water pressure of deep ocean depths, U.D.F. were guaranteed watertight to a depth of at least 100 meters (328 feet). Although watertight, the U.D.F. would only be mounted after coming to the surface, then before submerging, taken back inside. In case of a sudden emergency dive, the U.D.F. could be left behind on the conning tower.
Focus was fixed at the factory, and is not adjustable. A lever on the right prism housing was marked Hell (light) and Dunkel (dark) to set reticle illumination. In daylight, the knob is put in the Hell position, and the reticle is visible as a black vertical line. At night, the knob is put in the Dunkel position, and the reticle is visible as a white vertical line, illuminated by luminous paint. At the back is a bending bar for adjusting the eye position. U.D.F. have flip up rubber rear lens shields with side extensions to block light shining in from the sides. They are also equipped with small holes to drain condensation.
Original finish over the natural bronze construction is dark sea-blue enamel paint. The U.D.F. serial numbering system appears to be a special series for the Marine (Navy), or perhaps just for the Unterseebootdienst (Submarine Service, U-boat Service).
CARL PLATH / HAMBURG – Kriegsmarine sextant with Reichsadler over script “M” (Marine, Navy) and Kriegsmarine property number
CARL PLATH / HAMBURG – Kriegsmarine sextant – “D.S.” (Deutsche Seewarte), German Hydrographic Office, similar to the U.S. Naval Observatory) and C. Plath “Sonnenschiesser” (“Sun Shooter”) logo
16678 1630
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| S/N | Identifying Features | Year of Mfg | |||
| serial number 4796 |
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CP : 4796 mfg. about 1906 |
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| serial number 8340 |
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CP : 8340 mfg. about October 1920 |
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| serial number 12338 |
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CP : 12338 mfg. about January 1930 |
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| serial number 12557 |
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CP : 12557 mfg. about June 1930 |
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| serial number 16426 unit number |
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CP : 16426 Strm Sch 14 mfg. about 19xx |
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| Outside of black Bakelit (Bakelite) handle marked with round “C. PLATH / “Sonnenschiesser” / Hamburg” logo, and inside of handle marked “IRS” and horizontal oval surrounding “9366” and round “Ai / m / S” Bakelit composition logo.C. Plath logo on inside of handle and on zinc plate attached to inside lid of fitted wooden box. Serial number 16426 paperwork includes two calibration certifications from 1958 and 1960, plus US Customs certificate.
German Kriegsmarine sextants known to have belonged to specific units are very rare. This one (serial number 16426) reportedly belonged to U-291. U-291 was a Type VIIC U-boat of the German Kriegsmarine (1939-1945) during World War II. The submarine was laid down on October 17, 1942 at the Bremer Vulkan yard at Bremen-Vegesack as yard number 56. She was launched on June 30, 1943 and commissioned on August 4 under the command of Oberleutnant zur See Hans Keerle. U-291 served with the 21st U-boat Flotilla for training from August 4-31, 1943, and was a ‘trials boat’ with the 23rd Flotilla from September 1, 1943 to July 1, 1944. She then worked as a ‘school boat’ from July 1, 1944 to February 28, 1945, once more with the 21st Flotilla. Her last assignment was with the 31st Flotilla from March 1 to May 8, 1945. U-291 carried out no patrols and did not sink or damage any ships. The boat was surrendered on May 5, 1945 at Cuxhaven, Lower Saxony, Germany, on the shore of the North Sea at the mouth of the Elbe River. She was transferred on June 24 from Wilhelmshaven to Loch Ryan in Scotland for Operation Deadlight, and was sunk by the guns of HMS Onslaught off the coast of Northern Ireland on December 20, 1945. |
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| serial number 16678 unit number 1630 |
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CP : 16678 1630 mfg. about 19xx |
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| Outside of black Bakelit (Bakelite) handle marked with round “C. PLATH / “Sonnenschiesser” / Hamburg” logo, and inside of handle marked “IRS” and horizontal oval surrounding “9366” and round “Ai / m / S” Bakelit composition logo. | |||||
| serial number 17040 unit number 1033 |
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CP : 17040 1033 mfg. about 19xx |
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| Outside of black Bakelit (Bakelite) handle marked with round “C. PLATH / “Sonnenschiesser” / Hamburg” logo, and inside of handle marked “IRS” and horizontal oval surrounding “9366” and round “Ai / m / S” Bakelit composition logo. | |||||
| serial number 17562 unit number 1950 |
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CP : 17562 1950 mfg. June 1940 |
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| Outside of black Bakelit (Bakelite) handle marked with round “C. PLATH / “Sonnenschiesser” / Hamburg” logo, and inside of handle marked “IRS” and horizontal oval surrounding “9366” and round “Ai / m / S” Bakelit composition logo. | |||||
| serial number 17710 unit number 2048 |
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CP : 17710 2048 mfg. about August 1943 |
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| Outside of black Bakelit (Bakelite) handle marked with round “C. PLATH / “Sonnenschiesser” / Hamburg” logo, and inside of handle marked “IRS” and horizontal oval surrounding “9366” and round “Ai / m / S” Bakelit composition logo.KRIEGSMARINE MICROMETER SEXTANT BY CARL PLATH HAMBURG 1943
Kriegsmarine sextant of Plath in a ladder frame of black coated aluminum |
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| serial number 20274 unit number 4834 |
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CP : 20274 4834 mfg. about 19xx |
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| serial number 21375 unit number 4074 |
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CP : 21375 4074 mfg. about 19xx |
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| Outside of black Bakelit (Bakelite) handle marked with round “C. PLATH / “Sonnenschiesser” / Hamburg” logo, and inside of handle marked “IRS” and horizontal oval surrounding “9366” and round “Ai / m / S” Bakelit composition logo. | |||||
| serial number 21453 unit number 5992 |
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CP : 21453 5992 mfg. about November 1942 |
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| Outside of black Bakelit (Bakelite) handle marked with round “C. PLATH / “Sonnenschiesser” / Hamburg” logo, and inside of handle marked “IRS” and horizontal oval surrounding “9366” and round “Ai / m / S” Bakelit composition logo. | |||||
| serial number 21559 unit number 3369 |
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CP : 21559 3369 mfg. about November 1942 |
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| Outside of black Bakelit (Bakelite) handle marked with round “C. PLATH / “Sonnenschiesser” / Hamburg” logo, and inside of handle marked “IRS” and horizontal oval surrounding “9366” and round “Ai / m / S” Bakelit composition logo. | |||||
| serial number 22969 unit number 7382 |
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CP : 22969 7382 mfg. about 19xx |
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| Outside of black Bakelit (Bakelite) handle marked with round “C. PLATH / “Sonnenschiesser” / Hamburg” logo, and inside of handle marked “IRS” and horizontal oval surrounding “9366” and round “Ai / m / S” Bakelit composition logo. | |||||
| serial number 25294 unit number 9847 |
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CP : 25294 9847 mfg. about July 1944 |
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| serial number 27977 |
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CP : 27977 mfg. before August 1947
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| s/n 346100 |
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blc : 346100 mfg. about 19xx |
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| s/n 346126 |
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blc : 346126 mfg. about 19xx |
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| s/n 346215 |
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346215 | |||
| U-310s/n unknown
unit number 2143 |
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blc : s/n unknown mfg. about 19xx |
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| U-534s/n unknown
unit number 1554 |
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blc : s/n unknown mfg. about 19xx |
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xxx — Carl Plath, Stubbenhuk 25, Hamburg, Deutschland
Faking it. Is it a genuine C. Plath or is it a replica USSR SNO-M?
Figure 01 – Comparison of aluminum frame back of genuine CARL PLATH / HAMBURG Kriegsmarine Sextant vs. Russian SNO-M replica sextant
In my post for October 2008, I wrote about the USSR SNO-M sextant and gave my opinion that it was identical to the aluminum alloy-framed C. Plath sextant of WW II.
This was based on examination of photographs of putative WW II C. 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 USSR SNO-M frames, with the same pattern of sprues and risers from the casting process visible on the back of the frames (Figure 01).
I strongly suspect that these so-called C. Plath sextants are forgeries based on changing the obviously different USSR SNO-M index arm and engraving C. Plath logos and numbers on to the ends of the limb, which are conveniently vacant for them.
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.
Figure 02 – Comparison of aluminum frame back radii of genuine CARL PLATH / HAMBURG Kriegsmarine Sextant vs. Russian SNO-M replica sextant
This will not do, as there are other, more subtle differences, indicated in Figures 01 and 02, which show that even allowing for the traces of the casting process, differendies were used.
The dies used for pressure casting are very expensive to make, but are necessary when casting aluminium that could be expected to produce 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 labor shortages at this time.
03 – Cast into the interior of the genuine C. Plath mirror brackets are part numbers preceded by the initials “C. P.”, while no such numbers will be found inside USSR SNO-M brackets
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 03), while no such numbers will be found inside USSR SNO-M brackets.
04 – The foot of the USSR SNO-M horizon mirror bracket is displaced upward, obviously different than the centered foot of the genuine C. Plath horizon mirror bracket
The foot of the horizon mirror bracket is displaced upwards in the USSR SNO-M (Figure 04). 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.
05 – The index shades seem to be identical, except that the little brass knobs have a traditional, machined shape in the C. Plath but are simple, plain cylinders in the USSR SNO-M. The horizon shades seem identical, but their mountings are not. Difference are circled.
The index shades seem to be identical, except that the little brass knobs have a traditional shape in the C. Plath and are stark cylinders in the USSR SNO-M. Again the horizon shades seem identical, but their mountings are not. I have circled two points of difference in Figure 05.
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).
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.
The handle is less easy to fake. The genuine wartime C. Plath has the C. 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.
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.
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.