The P.11g “Kobuz” was an upgraded version of the P.11c, developed under Wsiewołod Jakimiuk. In 1937, plans to fit a more powerful Mercury VIII 840 hp engine were considered but initially abandoned because the speed increase would have been minimal.
When production of the Jastrząb fighter using this engine ended in April 1939, the Polish Air Force decided to use the 150 available engines for a new P.11 variant. An order for 90 P.11g aircraft was placed, and the first prototype—based on a P.11c airframe—flew in mid-August 1939. It passed military tests and was approved for production.
The outbreak of World War II prevented mass production. The sole prototype was evacuated to Lwów, then Wielicko near Kowel, armed, and pressed into service. It saw combat on 14–15 September 1939, achieving two aerial victories under Lt. H. Szczęsny, before being evacuated to Romania for continued use.