He joined the Polish Air Force in March 1939 and became a flying instructor. After the German invasion of Poland he appears to have flown reconnaissance sorties.
When Poland fell, Frantisek escaped to Romania, where he was interned. Once he was free he made his way to France via the Balkans and Syria, arriving there in early May 1940.
After the collapse of France, Frantisek arrived in England. He joined No 303 Squadron at Northolt on 2 August 1940, converting to Hurricanes with the squadron.
Frantisek is normally considered to be the highest scoring Allied pilot in the Battle of Britain, with 17 victories. On 2 September he claimed a Bf 109 destroyed, on the 3rd another, on the 5th a Bf 109 and a Ju 88, on the 6th a Bf 109, on the 9th a Bf 109 and a He 111, on the 11th two Bf 109s and a He 111, on the 15th a Bf 110, on the 18th a Bf 109, on the 26th two He 111s, on the 27th a He 111 and a Bf 110 and on the 30th a Bf 109 and probably another. Awarded the DFM on 17 September, he received his decoration from King George Vl at Northolt on 20 September. His portrait was done by Cuthbert Orde that month.
During a patrol on 8 October 1940, Frantisek was killed when his Hurricane crashed at Cuddington Way, Ewell, Surrey. He is buried in Northwood Cemetery, Middlesex.
