The MG13 was an air-cooled light machine gun that was briefly standard issue for the Wehrmacht. It operated using a short recoil system and fed from box magazines on the left side of the receiver. Contrary to common belief, MG13s were not made from Dreyse 1912 water-cooled guns. The operating mechanism of the two different designs is very similar, but the receiver structure is very different. It would not have been practical to retrofit a water cooled Dreyse into an MG13.
Also, it is important to note that the “13” designation was intended to mislead arms regulators during the inter-war years when Germany’s arms development was restricted by the Versailles Treaty. The MG13 was actually adopted in 1932. It remained in service only for a few years, being replaced by the MG34.
The MG13 initially was fed from 25-round box magazines. Later, a 75-round double drum was developed primarily for anti-aircraft use. This drum is not interchangeable with the MG34 and MG15 drums, however.