Originally designed by Beretta's chief engineer Tullio Marengoni in 1935, the Moschetto Automatico Beretta (Beretta Automatic Musket) 38, or MAB 38, was developed from the Beretta Modello 18 and 18/30, derived from the Villar Perosa light machine gun of World War I fame. It is widely acknowledged as the most successful and effective Italian small arm of World War II, and was produced in large numbers and in several variants. Italy's limited industrial base in World War II was no real barrier toward the development of advanced and effective small firearms since at the time most weapons did require large amounts of artisanal and semi-artisanal man-hours to be fine-tuned and made reliable by default. At this, Italian specialized workers excelled and the initial slow production ratio meant that the MAB 38 only became available in large numbers in 1943, when the fascist regime was toppled and Italy split between allied-aligned co-belligerent forces in the south, and German collaborationists of the Italian Social Republic in the north.
The MAB 38 was developed by Beretta in order to compete in the rich market of machine and sub-machine guns; it was a well-made and sturdy weapon, introducing several advanced features, to be suitable for police purposes and special army units. Presented to Italian authorities in 1939, its first customer was the Italian Ministry of Colonies, which purchased several thousands MABs to be issued as standard firearm of the Polizia dell'Africa Italiana (Italian Africa Constabulary), the government colonial police force. However, army orders were slow to come: although impressed by excellent overall qualities and firepower of the weapon, Italian military did not feel the MAB could be suited for standard infantry combat. It was judged ideal for police and assault units, though, and in the beginning of 1941 small orders were placed for Carabinieri (military and civilian police), Guardie di Pubblica Sicurezza (national state police), and paratroopers. The Italian Army requested minor changes to reduce production costs, notably the changed shape recoil compensator and the removal of the bayonet and its catch. The weapon so changed was named MAB 38A. This was the standard army variant, used throughout all the war, and issued to the most elite Italian units: paratroopers, Alpini "Monte Cervino" assault battalion, 10th Arditi Regiment, "M" Battalions of MVSN, military police etc.
Italian Royal Navy also purchased it, and MAB 38A was given to "San Marco" Marine Regiment, and to naval security troops; The Regia Aeronautica (Italian Royal Air Force) issued the MAB 38A to its crack A.D.R.A. Regiment. Nevertheless, the Beretta MAB was ordered in relatively small quantities and standard Carcano M1891 rifle remained as standard weapon even of elite Italian units. Until 1943, MAB 38A (and, since 1942, the MAB 38/42) was available almost exclusively to paratroopers, Blackshirts, tank crews and Carabinieri military policemen, given the need of all of the former to express high volumes of firepower in prolonged actions or to keep close-quarters combat superiority. The standard paratrooper of the Folgore airborne division was armed exclusively with this weapon, and the division gave outstanding combat results. Similarly, Blackshirt legions (one per infantry division) were regarded and used as elite assault units both for their fanaticism and their armament, in which the Beretta 38 bulked.
It was after the Italian armistice of September 8, 1943, when Italian armed forces melted away and an Italian army was reconstructed in northern Italy under German sponsorship, that Beretta MAB found a widespread diffusion. The R.S.I. army, since its inception, was heavily engaged in guerrilla warfare against partisans, as well as in combat against the Allies; for assault and counterinsurgency units, where firepower at close range was a vital asset, this was the ideal weapon. Thus, production of MAB became priority, and it was supplied in large quantities to all R.S.I. formations, especially elite ones: paratroopers, Marine Infantry, "Arditi" and Assault Battalions, Republican National Guard, etc. and it became an iconic weapon, symbolizing the Italian soldier in popular culture. Later in the war, a more simplified variant known as 38/44 was introduced, with further solutions to speed up production and reduce costs. Regardless of the tables of organization and equipment of a given unit, the Beretta 38 was a popular weapon that could eventually find its way into the hands of virtually any soldier, especially amongst officers and higher non-commissioned officers, notably in Bersaglieri light infantry, artillery and armoured units. However, this weapon remained a rare view amongst common infantry and Alpini mountain infantry.
Italy developed a dedicated magazine-holding vest for elite troops (Blackshirts, paratroopers) armed with the Beretta 38; these were dubbed "Samurai" due to the aesthetic similarity of the stacked magazines with traditional Japanese armour. Furthermore, a special canvas holster was issued with the MAB, that featured two magazine-carrier pouches sewn onto it and that was meant to be thus worn as a belt. However, both these only came into use during the brief life of the R.S.I. and by then could be seen in the employ of many different units whose "elite" status could have been reasonably questioned (such as Black Brigades and other militias).
Beretta MAB was highly praised by Italian resistance movement fighters as well, being far more accurate and powerful than the British Sten wich was common issue in partisan units, although Sten was more suited for clandestine operations thanks to its more compact size. German soldiers also liked the Beretta MAB, judging it large and heavy, but reliable and well made.
The 1938 series was extremely robust and proved very popular with both Axis forces as well as Allied troops, who utilized captured examples. Many German soldiers, including elite forces such as the Waffen-SS and Fallschirmjäger forces, actually preferred to use the Beretta 38 in combat. Firing a powerfully loaded Italian version of the widely distributed 9×19mm Parabellum cartridge, the Cartuccia 9mm M38, the Beretta was accurate at longer ranges than most other submachine guns. The MAB could deliver an impressive firepower at close range, and at longer distances its size and weight (that was its only drawback compared to other similar guns) was an advantage, getting the weapon very stable and easy to control. In expert hands, the Beretta MAB allowed accurate short-bursts shooting up to 100 meters, and effective range, with Italian M38 ammunition, was 200 meters, an impressive result for a 9mm submachine gun.