Question: What cartridge, also known as 9 mm Luger by the C.I.P. or 9 mm NATO by NATO, is used in the submachine gun the MP 40?
Context: The M56 submachine gun is a Yugoslavian submachine gun chambered in 7.62×25mm Tokarev, designed for use with the Yugoslav People's Army.  Initially a state-funded product, it was later produced by Zastava Arms and saw use in a number of conflicts following the breakup of former Yugoslavia.  The M56 is a clone of the MP 40 submachine gun used by Nazi Germany, easily distinguished from the MP 40 by its increased length and curved magazine. The 9×19mm Parabellum, also known as 9 mm Luger by the C.I.P. or 9 mm NATO by NATO (abbreviated 9mm, 9mmP, 9×19mm or 9×19) is a cartridge that was designed by Georg Luger and introduced in 1902 by the German weapons manufacturer Deutsche Waffen und Munitionsfabriken (DWM) (German Weapons and Munitions Factory) for their Luger semi-automatic pistol. The SIG Sauer P290RS is a polymer frame pistol with a stainless steel slide.  It is chambered in 9mm Parabellum (aka 9MM Luger, 9mm Kurz).  It is a compact handgun suitable for concealed carry.  The finish is SIG Sauer's Nitron finish.  The side panels can be interchanged for a custom appearance.  The trigger is a Double Action Only (DAO) model with restrike capability.  Hence the RS designation in the model number. The MP 40 ("Maschinenpistole 40") was a submachine gun chambered for the 9×19mm Parabellum cartridge.  It was developed in Nazi Germany and used extensively by the Axis powers during the Second World War. The .380 ACP (9x17mm) (Automatic Colt Pistol) is a rimless, straight-walled pistol cartridge developed by firearms designer John Moses Browning.  The cartridge headspaces on the mouth of the case.  It was introduced in 1908 by Colt, for use in its new Colt Model 1908 pocket hammerless semi-automatic, and has been a popular self-defense cartridge ever since, seeing wide use in numerous handguns (typically smaller weapons).  Other names for .380 ACP include .380 Auto, 9mm Browning, 9mm Corto, 9mm Kurz, 9mm Short, 9×17mm and 9 mm Browning Court (which is the C.I.P. designation).  It is not to be confused with .38 ACP, 9mm Ultra, 9×18mm Makarov, 9×19mm Parabellum nor the rimmed .380 Long Revolver CF & .380 Rook Rifle cartridges, introduced around 1870. The Arsenal M23 submachine gun (Estonian: "Arsenali püstolkuulipilduja" ) (also known as Arsenal Tallinn) was an Estonian submachine gun from 1926 through 1935.  These submachine guns were designed and produced in the Estonian military equipment factory "Arsenal" in Karjamaa, Tallinn, but production was not more than 600 units.  The weapon was chambered for the 9x20 mm semi-rimmed Browning cartridge to be compatible with ammunition for the Browning FN M1903 pistol which had been adopted by the Estonian Army.  It operated on the blowback system and was essentially similar to the MP18.1; having a wooden stock, slotted barrel jacket, and horizontal left side magazine feed.  A uniquely slender 40 round single column box magazine led to frequent cartridge feeding problems; and cooling fins which were machined lengthwise along the barrel to promote cooling air flow when firing (similar to the Lewis machine gun), unnecessarily complicated production.  It was used by the combat support units of the Border Guard, the Estonian Defence League and the Estonian Defence Forces.  The Arsenal submachine gun was replaced in Estonian service by the Finnish Suomi KP/-31 submachine gun in 1938.  The Estonian Army sold a few samples to Latvia and all of the remainder found their way to Republican forces during the Civil War in Spain. The MP-446 Viking is a 9mm semi-automatic handgun originating from Russia.  It was created by the Izhevsk Mechanical Plant, located in Russia.  It weighs at around 830 g when unloaded, and has a magazine capacity of 18 rounds.  The pistol is a sport/civilian version of Yarygin PYa (MP-443) pistol which has been used by Russian military since 2003.  MP-446 is short recoil-operated, locked breech pistol.  The key differences between MP-446 and MP-443 are the frame material (polyamide rather than steel) and barrel construction: the barrel of the MP-446 was intentionally weakened to prevent safe use of high-powered armour-piercing military rounds (i.e. Russian 9x19mm 7N21 type, 9x19mm NATO) or civilian "+P" or "+P+" cartridges.  For civilian use, the pistol can only be loaded with 10 rounds of 9mm Luger. The .30-06 Springfield cartridge (pronounced "thirty-aught-six" or "thirty-oh-six"), 7.62×63mm in metric notation and called ".30 Gov't '06" by Winchester, was introduced to the United States Army in 1906 and later standardized; it remained in use until the early 1980s.  The ".30" refers to the caliber of the bullet.  The "06" refers to the year the cartridge was adopted—1906.  It replaced the .30-03, 6mm Lee Navy, and .30-40 Krag cartridges.  The .30-06 remained the U.S. Army's primary rifle and machine gun cartridge for nearly 50 years before being replaced by the 7.62×51mm NATO (commercial .308 Winchester) and 5.56×45mm NATO, both of which remain in current U.S. and NATO service.  It remains a very popular sporting round, with ammunition produced by all major manufacturers. The 9×18mm Makarov (designated 9mm Makarov by the C.I.P. and often called 9×18mm PM) is a Russian pistol and submachine gun cartridge.  During the latter half of the 20th Century it was a standard military pistol cartridge of the Soviet Union and the Eastern Bloc, analogous to the 9×19mm Parabellum in NATO and Western military use. The Pistol Mitralieră model 1996 RATMIL (also called the "RATMIL model 96") is a blowback operated, folding stock submachine gun chambered in 9mm Luger used by the Romanian gendarmes.  Initially developed as the 9mm PM md. 96, the developer's name, back then RATMIL, was added to the name, in order to distinguish it from the Assault SMG, also called PM md. 96.
Answer: 9×19mm Parabellum