The AK-47 is a selective-fire, gas-operated 7.62×39mm assault rifle, first developed in the USSR by Mikhail Kalashnikov. It is officially known as Avtomat Kalashnikova. Design work on the AK-47 began in the last year of World War II (1945). The original AK-47 was one of the first assault rifles of 2nd generation, after the German StG 44. Even after six decades the model and its variants remain the most widely used and popular assault rifles in the world because of their durability, low production cost, and ease of use.