The PZL P.11 fighter was a development of Zygmunt Puławski’s P.6 design. After Puławski’s death in 1931, engineer Wsiewołod Jakimiuk continued the project, adapting it for a more powerful 700-hp engine. Despite continuous prototype modifications, the aircraft achieved success at international competitions in Zurich (1932) and Cleveland, bringing global attention and foreign interest.
In 1933 the P.11a, powered by a Bristol Mercury IV engine, was developed for the Polish Air Force. After successful testing, 50 aircraft were ordered, though production was delayed by Romanian orders for the P.11b. The P.11a entered Polish service in 1934 and remained in use through the 1939 Defense War, fighting from the first day until evacuation after the Soviet invasion. Surviving aircraft were interned in Romania for training use, and one later served in Hungary as a glider tug. No P.11a survives today.
The PZL.37 Łoś was a modern Polish twin-engine medium bomber designed in the mid-1930s by Jerzy Dąbrowski. Early prototypes had a single tail, while later A and B versions adopted a twin vertical stabilizer arrangement. Serial production began in 1938, and the aircraft was considered one of the most advanced bombers of its era. The Łoś served in the 1939 campaign; 26 were evacuated to Romania and subsequently taken into Romanian service, while others were examined by Germany and the USSR after capture.