The Astra Model 900 is one of many Spanish copies of the German Mauser C96 semi-automatic pistol. It shares the same caliber, magazine capacity, and holster type and is generally very similar to the German handgun.
The Basque-manufactured Astra-Unceta y Cia SA Astra 901 is a compact machine pistol, with a magazine capacity of 10 7.63x25mm Mauser cartridges, which is a considerably smaller capacity than is standard for a machine pistol. The next model, the Astra 902, was provided with a fixed magazine of 20 cartridges and a lengthened barrel, and Astra 903 had a removable magazine instead of the usual fixed one. Astra later added a mechanism to slow the rate of fire and make the gun more manageable (to an extent) when being fired on full-auto or burst modes, calling this the Model 904. The Model 904 is comparable to the German Mauser M712 'Schnellfeuer' Broomhandle pistols, having a detachable magazine, automatic fire capabilities, and general appearance.
The Astra Model 904 was produced in a 9 mm Largo variant, the Astra Model 904E, which was identical to the Model 904 in all other respects.