German machine gun designations are pretty easy to understand – the two digit number is the year of adoption. MG34? 1934. MG08/15? 1908, and modified in 1915. Easy, until you stumble over the MG13, adopted in 1932.Imagine that you are the Wehrmacht, and your wife is the Allied commission in charge of enforcing Versailles arms restrictions, who has just caught you sneaking in the house with your fancy new MG13. “That one? No, dear, I didn’t just buy that – it’s just been in the back of the safe since, um, 1913. You just never noticed it before. Really!” That didn’t last very long, though, before Germany stopped trying to hide its rearmament at all, and dropped the MG13 in favor of the MG34.
The MG13 was a developmental successor to the Dreyse 1912 water-cooled machine gun (which saw use in WWI, but was overshadowed by the 08 Maxim). The internals of the two guns are very similar, and a lot of internet sources say that the water cooled guns were modernized and retrofitted into air-cooled MG13s. This is not true; the receivers are not at all interchangeable – MG13s were built from scratch.
We now have an MG13 page in the Vault, and have a Spanish language manual on the gun available there.