There are a fewexamples where the real name of a tank or gun sinks into the sands of time, replaced by a more popular, yet incorrect one. The Renault FT is another example. More often than not, you see the tank called "FT-17", rarely "FT-18". Looking at production codes at Renault, the number was never included. For example, the Renault FT was preceded by the Renault FS, a car, and succeeded by the Renault FU, a heavy truck. However, even serious sources attach a number to the tank's name. Where did the number come from?
German documents regarding the Renault FT use the extra numbers.
The answer, in this case, is relatively simple. A tank encyclopedia called Taschenbuch der Tanks was written in 1935. The book was very popular at the time, and was considered a reputable source. Unfortunately, the authors filled it with a number of their own fabrications. For example, the names "Renault M.17 F.T." and "Renault M.18 F.T." were invented to differentiate between tanks with a cast riveted turret and cast turret respectively.
Russian translation of Taschenbuch der Tanks. The "M 17" with a riveted turret is on the left, the "M 18" with a cast turret is on the right. In reality, both tanks were simply designated "Renault FT".
This is far from the only fabrication in the encyclopedia. Readers can also read about mythical vehicles like the French "Heavy tank D" with a crew of 15 men and four cannons, a number of made up export tanks and incorrect destinations for real ones, various other mistakes with indexes, etc. Nevertheless, the information in this encyclopedia was taken at face value at the time and influenced the development of tank building in several countries.