In 1937 Böhm applied for patent #DE703 133. It was granted in 1941. The idea was to use a slider to cover one set of reeds instead of shifting an entire reed plate as described in the earlier patent #DE470354 by Otto Hermann Böhm and applied in earlier Böhm models.
The newly patented idea was then realized in several new Böhm chromatic models.
The Blue Bird Chromatic Vamper was a single tone chromatic harmonica. As you can see in the below manual the notes were in a particular order.
The Tremolo Chromatic, also manufactured by Böhm, followed the same principle of covering one set of reeds.