7,62 ITKK 31 VKT or 7,62 mm VKT anti-aircraft machine gun was the primary anti-aircraft machine gun of the Finnish Army during World War II.
 The weapon was designed by the Finnish gunsmith Aimo Lahti.
 507 weapons were produced in two versions, 7,62 ItKk/31 VKT and an improved 7,62 ItKk/31-40 VKT, between 1933 and 1944.
The United Defense M42, sometimes known as the Marlin for the manufacturer, was an American submachine gun in World War II.
 It was produced from 1942 to 1943 by United Defense Supply Corp.
 (a government-formed company specifically tasked with weapons development) for possible issue as a replacement for the Thompson submachine gun and was used by agents of the Office of Strategic Services (OSS).
Aimo Johannes Lahti (April 28, 1896 – April 19, 1970) was a self-taught Finnish weapons designer.
 Of the 50 weapons he designed, the best known is the Suomi M-31 SMG.
 Other well-known weapon designs of his include the Lahti-Saloranta M/26 LMG, Lahti L-35 pistol, and Lahti L-39 anti-tank rifle.
 Lahti also designed the 7,62 ITKK 31 VKT anti-aircraft machine gun and the 20 ITK 40 VKT anti-aircraft cannon.
The Suomi KP/-31 (Suomi-konepistooli or "Submachine-gun Finland", literally: "Machine-pistol Finland") was a submachine gun (SMG) of Finnish design used during World War II.
 It was a descendant of the M-22 prototype and the KP/-26 production model, which was revealed to the public in 1925.
 The "Suomi-konepistooli KP/-31" is often abbreviated to "Suomi KP".
The MP 18 manufactured by Theodor Bergmann "Abteilung Waffenbau" was the first submachine gun used in combat.
 It was introduced into service in 1918 by the German Army during World War I as the primary weapon of the "Sturmtruppen", assault groups specialized in trench combat.
 Although MP 18 production ended in the 1920s, its design formed the basis of most submachine guns manufactured between 1920 and 1960.
20 ItK 40 VKT or "20 mm dual anti-aircraft cannon model 1940 manufactured by VKT" was a Finnish light anti-aircraft gun designed by the Finnish gunsmith Aimo Lahti.
 As the only multi-barrel 20 mm anti-aircraft gun 20 ItK 40 VKT was the most effective 20 mm air defence weapon used by the Finnish Army during World War II.
 A total of 174 guns were built, used in training until the 1970s and kept in reserve until 1988.
 The gun received the nickname "Vekotin" (gadget) from Finnish soldiers.
 The nickname was reached by adding to the abbreviation of manufacturer, VKT.
The MAS-38 was a French submachine gun designed prior to the Second World War and used by French and German forces.
 It was derived from a small arms development program that took place between 1918 and 1922 under the control of the Service Technique de l'Armement.
 A submachine gun, a light machine gun and a semi automatic rifle were developed to replace all the existing small arms.
 Budgetary constraints due to choices like building the Maginot Line led to the delay of adoption of these new arms except for the LMG 1924.
The Owen Gun, which was known officially as the Owen Machine Carbine, was an Australian submachine gun designed by Evelyn (Evo) Owen in 1939.
 The Owen was the only entirely Australian-designed and main service submachine gun of World War II and was used by the Australian Army from 1943 until the mid-1960s.
The Type 100 submachine gun (一〇〇式機関短銃 , Hyaku-shiki kikan-tanjū ) was a Japanese submachine gun used during World War II, and the only submachine gun produced by Japan in any quantity.
 It was made in two basic variants referred to by American and British observers as the Type 100/40 and the Type 100/44, the latter also known as the Type 100 (Simplified).
 A third variant was a folding version of the early model, sometimes referred to as the Type 100 Navy, made for parachutists.
Pistolet maszynowy wz.
 39 Mors ("Mors" is Latin for "death", Polish for "walrus") was a Polish submachine gun designed by Piotr Wilniewczyc and Jan Skrzypiński between 1936 and 1938.
 It was to have become the standard submachine gun of the Polish Army some time in the 1940s.
 However, its production was halted by the 1939 Invasion of Poland and World War II.

Question: What was the name of the submachine gun used during World War II, that was designed by Aimo Lahti?
Answer: Suomi KP/-31