1915[1] (Commonly known as the Beretta Model 1918) was a self-loading carbine that entered service in 1918 with the Italian Armed Forces.
[3] In the 1930s the semiautomatic[4] Mod.1918/30 model was developed; It completely revamped the action of the gun, replacing the delayed-blowback Villar Perosa action with a new closed-bolt system with a loose firing pin that was cocked by a guided rod protruding from the rear of the receiver, with a ring-shaped cocking piece.
[5] While the standard Revelli-Beretta carbine was a semi-automatic weapon only, several experimental variants were developed with selective-fire capability.
This type of trigger group became standard on later Beretta submachine guns, including the well-known Model 38 series.
The exact reason for the development of the MIDA submachine gun is still not entirely known but it was probably for a special military contract from some unit that desired a variant of the Revelli-Beretta carbine with automatic fire capability.