Vis is a 9 mm caliber

Caliber

In guns including firearms, caliber or calibre is the approximate internal diameter of the barrel in relation to the diameter of the projectile used in it....

, single-action, semi-automatic pistol. Originally designed by Piotr Wilniewczyc

Piotr Wilniewczyc

Piotr Wilniewczyc was a Polish engineer and arms designer. Among his most successful designs were the Vis-35 pistol, commonly known as the Radom for the arsenal in which it was produced, and the Mors submachine gun.- Biography :...

 and Jan Skrzypiński in 1930 at the Fabryka Broni (Weapon Factory) Łucznik Arms Factory in Radom

Radom

Radom is a city in central Poland with 223,397 inhabitants . It is located on the Mleczna River in the Masovian Voivodeship , having previously been the capital of Radom Voivodeship ; 100 km south of Poland's capital, Warsaw.It is home to the biennial Radom Air Show, the largest and...

 under Director Kazimierz Ołdakowski, it was adopted in 1935 as the standard handgun of the Polish Army. Considered by many to be one of the finest handguns ever produced, it is highly prized among collectors of firearms.
The design was generally based on American firearms inventor John Browning

John Browning

John Moses Browning , born in Ogden, Utah, was an American firearms designer who developed many varieties of military and civilian firearms, cartridges, and gun mechanisms, many of which are still in use around the world...

's Colt M1911A1, operating on the short-recoil principle, with the barrel being cammed down and away from the locking lugs in the slide.