One of the (many) reasons to follow the WeaponsMan blog is that he keeps an eye out for neat auctions that, even if they cost the same as a new luxury sedan, provide great photos of rare or unique firearms. Most recently, Hognose has linked to an auction for a very rare MP.18-I, the first variant of the famous German MP.18 submachine gun (which, arguably, was the progenitor of the type):

We’ve featured an MP.18-II before, which is a later iteration of this exact same gun, with a magazine well reconfigured for straight magazines. (It led in turn to the MP.28, the Lanchester, and the Sten, by fairly direct process of derivation). But this gun, the MP.18-I, is the granddaddy of them all, and it could be yours.

It is certainly the first widely produced submachine gun, defined as a shoulder-fired infantry weapon firing a pistol cartridge with an automatic or select-fire mechanism. A blowback mechanism, it showed the way for many designs that would follow through three generations of submachine guns, until the rise of compact versions of intermediate-cartridge assault weapons would replace most of them.

Some would say it has a face only a mother could love:

And it’s just as awkward looking from behind. 

The drum magazine is so odd looking because it was already in production for the Lange P.08, the “Artillery” Luger. Rather than try to design a thirtyish-round magazine, the engineers at Theodor Bergmann in the weapons-manufacturing center Suhl, Germany, did what many later gun designers would do and borrowed a proven one.

The only real predecessor to the MP.18 was the Villar-Perosa, which in its original configuration was an aircraft automatic gun chambered for pistol rounds, but later was applied to ground warfare as a light machine gun, and eventually as a portable automatic weapon. However, the Villar-Perosa, besides not being widely issued and not being purpose-designed as a submachine gun, was also much less influential; the descendants of the MP.18 being outright copied by many nations even as late as the 1940s.

I highly recommend readers follow the link and take a look at the auction itself; more pictures are available there (unfortunately in relatively low-res).