The Błyskawica (Polish for "lightning", pronounced buy-ska-vit-tsa) submachine gun was designed and used by the Polish resistance movement during World War II. Its external layout was modeled after the MP-40, while most of internal mechanisms were copied from the Sten. Often produced in primitive conditions and without advanced tools, those weapons offered surprisingly good performance and reliability. It was used in Operation Tempest, the Warsaw Uprising, and in a number of smaller sabotage actions. Around 700 of them were built.