In 1942 Charvin took out a patent showing a version of its late 1930s Charvin Le Lautaret derailleur with a thinner main cylinder and its cable fed over a roller, rather than through a curved tube. I, therefore, think that this particular example dates from around that time. It can certainly claim to be lighter and neater than the earlier version.
As with the late 1930s design, this was a fairly well made, simple, mechanism with a distinctively offset pulley cage. The sliding rod and the spring that controlled the movement in and out were both reasonably well sealed. This was probably quite a good design for maintaining a reasonably constant chain gap.
This particular example has a silver pulley cage, black 28mm diameter pulleys, 12mm pulley bot nuts, no cable adjuster and a roller to direct the cable.