The P-47 Thunderbolt was designed by Alexander Kartveli, a man of Georgian descent. It was to replace the Seversky P-35 developed earlier by a Russian immigrant named Alexander P. de Seversky. Both had fled from their homeland, Tbilisi, in Georgia to escape the Bolsheviks. In 1939, Republic Aviation designed the AP-4 demonstrator powered by a Pratt & Whitney R-1830 radial engine with a belly-mounted turbocharger. A small number of Republic P-43 Lancers were built but Republic had been working on an improved P-44 Rocket with a more powerful engine, as well as on the AP-10 fighter design. The latter was a lightweight aircraft powered by the Allison V-1710 liquid-cooled V-12 engine and armed with two .50 in (12.7 mm) M2 Browning machine guns mounted in the nose and four .30 in (7.62 mm) M1919 Browning machine guns mounted in the wings. The United States Army Air Corps (USAAC) backed the project and gave it the designation XP-47.