Minox incorporated as it's own company in Germany in late 1945, amidst the ruins of World War II. The Model II represented a first for the new company in several respects: although a few were initially constructed from stocks of Riga Minox parts, they soon switched over to aluminum body shells, making them significantly lighter; they were the first to incorporate two, built in , sliding filtres (yellow and green, and later, green and orange); they were the first and only model to incorporate the 5 element, Pentar "film plane" lens design; and, at various stages in their production, were the first and only models of Minox 9.5mm cameras to have a milled in, removable hatch to allow access to the lens chamber for shutter speed testing using a tiny periscope type device specially made for this purpose.
This was because the original shutter blades were black, and could not reflect light well. Later model Minox cameras used silver coloured shutter blades which reflected light quite well, allowing the use of an external measuring device to determine the accuracy of the shutter speed settings by Minox technicians. It has been erroneously reported in more than one book that this hatch was designed to allow the user to clean the film lens, but as Donald Goldberg pointed out to me, the lens chamber is essentially a sealed unit and would not have allowed dust to enter in the first place; the user would never have had a need to open the hatch. The side of the lens that might have needed cleaning (the side in contact with the film) was actually facing out on the film chamber.
Donald Goldberg also provided the fascinating tidbit of information that apparently more than a few Model II cameras were made from the aluminum skin of downed aircraft: due to the extreme shortage of raw materials right after World War II, the aluminum recovered from these aircraft provided a cheap (free) source of material for the body shells. This information was given to him in conversation with one of the very first German employees of the (then) newly formed Minox, Gmbh, during Donald's time working for them.
Designed by Arthur Seibert in response to Walter Zapp's desire to eliminate curvilinear distortion (the slight loss of sharpness at the edges of a photograph from the original Riga Minox lens design), the Pentar lens can only be considered now as a poor design. Essentially, the film was curved around the rearmost glass element of the lens, in full physical contact with it. It stayed in contact with the lens during the film advance cycle, dragging it across the lens and quite often horribly scratching the negatives in the process.
The poor reputation of this lens design was such that when Seibert later produced his superb Compensating Plane lens (Complan) Minox quietly retrofitted many Model II's with them as they came back for service or cleaning. Consequently, although the Complan Lens design was officially introduced in the Model III camera, there exist a small number of converted Model II's. For a look at what a Model II looks like, see the section on Model III: the two cameras appear physically identical on the outside, other than model markings on the bottom deck.
This camera became known as the "Model II" retroactively, after the introduction of the Model III; previously, it had merely been known as a "Minox" camera.