German saxophone manufacturers are a bit difficult to learn about, primarily because a lot of the documentation has been destroyed either in the manufacturer's move from one part of Germany to another or in the WWII and the conversion of many of the music instrument factories over to producing war materiel.

 This brings us to Kohlert.

A brief digression: Kohlert is NOT Köhler. Köhler was founded in Markneukirchen, Germany in 1933 by Franz Köhler.  They stopped producing instruments around 1961 [1] .

(However, while the Köhler example I've seen does not look like a Keilwerth or Kohlert design, yes, there's always the possibility that Köhler did stencil some horns from either Keilwerth or Kohlert.)

The similarity in names and similarity in the saxophone designs from Kohlert and Köhler throws most folks for a considerable loop.  The similarity in design is not because they shared a common ancestor, but more rather because company X would produce a good design and then everyone else would copy it (this tidbit of information popped up numerous times while I researched Kohlert and Keilwerth).  Matters grew more complicated after Keilwerth began producing saxophones in 1925/6: not only did Keilwerth produce stencils of their horns (of which, they branded at least one Kohlert model), but they furnished saxophone bodies to a variety of other German and Czech manufacturers which would affix their own keywork and sell the horn under a different name - sometimes with no trace of the Keilwerth mark on the horn.

However, Kohlert IS "Vincenta (or "V." or "Vizenze" or several other variants) Kohlerta Synové Kraslice".  This is the Czech form of Kohlert's name.  There are other Anglicized/Germanized variants of the VKS label (e.g. "V. Kohlert's Sons"), but some variant of "Kohlert" is always listed.

Here's a timeline:

1840: The Kohlert Company was founded in Graslitz, Czechoslovakia by Vincenz Ferarius Kohlert [2] .  However, he did not produce any saxophones.

1900/01: V.F. Kohlert dies and the ownership of the Kohlert Company is transferred to his sons, Rudolf, Daniel and Franz [3] and the company's name is changed to "V. Kohlert's Söhne".  Kohlert produces the first German-made saxophone around this time [4] .

1910-1916 (Approximately): Kohlert stencils saxophones for HN White (King) in the USA [5] .

1914-1925 (Approximately): Julius Keilwerth apprentices at the Kohlert company.  It is arguable if Keilwerth influences Kohlert's designs more or vice versa [6] .

1938 (Approximately): Kohlert has become the largest German instrument maker, employing 600 craftsmen and producing an entire range of brass, woodwind and double-reed instruments [7] .  Keilwerth is a distant second with 150 craftsmen and producing only saxophones.

1939-1945 (Approximately): WWII.  Kohlert produced relatively few instruments during this time, as production was limited by the conversion of most factories to producing war materiel and the Nazi original disgust of all things Western, especially jazz.  There was some limited production and some horns produced during WWII are labeled "Reich" and are quite elaborately engraved - with Nazi regalia.

1945-1947: After WWII, the firm was "nationalized" into the Amati cooperative [8] (Amati's website says the cooperative was founded in 1945 and was fully "nationalized" by 1948 [9] ) and the Kohlerts became workmen in their own factory, similar to what happened with the Keilwerth family.  According to the Lein article, the Kohlert family was no longer even allowed to put their stamp on their instruments [10] .

It's an unconfirmed fact that Amati used Kohlert and Keilwerth tooling in their first horns, rather than producing anything new: the first Amatis were labeled "Toneking" - a Keilwerth model name - and had the Keilwerth "Best in the World" logo stamped on the back.  Some even used the Keilwerth serial number chart! 

I'm not quite sure if Amati just decided to use Keilwerth saxophones as their template for future models, but the "second generation" of Amati horns, such as the "Classic Super" is fairly reminiscent of Kohlert, not Keilwerth, designs.

1948: The "last" generation of the Kohlerts migrated ("evacuated" would be more accurate, according to the Lein article) to West Germany:  Max Kohlert, an instrument maker, died in 1949. Kurt Kohlert, a businessman, died in 1973. Ernst Kohlert, a musician, died in 1986 or '87. None of the three brothers ever married.

After arriving in the West, Ernst worked for a short while with instrument makers near Fürth.  Shortly thereafter, the city of Winnenden provided the brothers with a former barracks (actually a wooden house) in which to establish a new workshop [11] .

1948/49: About forty people were employed in the Winnenden factory. At first, they only repaired instruments, mainly for the American army [12] , but resumed instrument production began in the fall of 1949 with saxophones. A new serial number chart was instituted, starting at zero [13] and the "V. Kohlert's Söhne" mark was dropped in favor of just "Kohlert".

Cybersax.com and a few miscellaneous newsgroup/forum posts also indicate that there was a Kohlert model that had beveled tone holes, like the Martin and early Couesnon horns .  Considering this design is a radical departure from the standard Kohlert designs AND because Keilwerth also produced a similar design right after they fled Czechoslovakia, it's possible that either this "new" model is either a Keilwerth design or could have been jointly developed between the two companies (there is a suggestion that the bodies were imported from the Martin company, but that's a bit of a stretch and there's nothing to corroborate this suggestion).

1953/54: Kohlert employed around 100 people from 1953 to 1954, with about seventy working in the "barracks" and another thirty working at home [14] . These "home workers" had small shops in their homes and would receive the materials, complete their part of the assembly process and return them. Several craftsmen only made saxophone bodies and even the bells and necks were made in Winnenden [sic]. The Kohlerts also employed four tool-makers whose job it was to make the tools and apparati used in the factory according to the designs and needs of the instrument makers. Thus everything was done "in house" with specially crafted tools [15] .

1955-1965: The two remaining Kohlert brothers, Kurt and Ernst, entered into contracts with American wholesalers [16] which guaranteed that the Kohlerts would supply instruments at the same price for ten years [17] . What the brothers didn't foresee was the onset of the "Deutsche Wirtschaftswunder," or "German economic miracle", when the materials costs and wages rose dramatically. At this point they couldn't get out of these long-term commitments -- the penalty for breach of contract was severe.

Instead of specializing on a single instrument, like the Julius Keilwerth company, Kohlert continued to make the whole range of instruments - and, so the profit margin kept shrinking. Realizing they couldn't continue in this manner, Kohlert tried to cut labor costs by minimizing handwork and started mass-producing hundreds of parts. This idea didn't work and left Kohlert with a financial situation which required declaring bankruptcy in 1965 [18] .

1966: About twenty employees continued producing instruments to meet bankruptcy obligations. Serial numbers stood at about 85,000 at the time of the bankruptcy.

1967: Fritz Pfannenschwarz, an industrialist from Nordheim who was interested in music as a hobby, came to Kohlert to buy a bass clarinet and was told that nothing could be sold without consulting the administrator of the bankrupt estate. He asked the price of the bankrupt firm, was told 40,000 DM and subsequently bought it. Although plans had already been drawn for a new factory, nothing had come of them and work continued in the "barracks". Later Pfannenschwarz moved final assembly operations and sales to Nordheim, concentrating on flutes, saxophones and clarinets [19] .

ERRATA:

* Contrary to some Internet forums and newsgroups, I see no relation between SML and Kohlert.  The connection that people use between the two companies is that both used rolled tone holes and that some Kohlert models are said to have the "switchable" articulated G# key.  Literally dozens of companies used rolled tone holes and Leblanc/Beaugnier/Vito used the switchable G#, too, and none of these have any connection to SML.  Additionally, I can't really see a French manufacturer cooperating that closely with a German manufacturer around WWII (SML was founded in the late 1930's).

* There has been a lot of discussion about the Kohlert model that has the fancy little letter keyguards.  First of all, the letters are "VKS", not "JSK", and it probably stands for "V. Kohlert's Söhne". The "JSK", in this interpretation, is expanded to mean "Julius S. Keilwerth".  I've not found any documentation that even says that Julius' middle name started with an "S" and the mark on Keilwerth horns is "JGK: The best in the world."