Complex sentence: During the Invasion of Poland in 1939 Urbanowicz was in an improvised Ulez Group, comprising of flying instructors, flying obsolete PZL P.7a fighters and covering the Dęblin and Ułęż airfields.
Split into simpler sentences: During the Invasion of Poland in 1939 Urbanowicz was in an improvised Ulez Group, comprising of flying instructors. They were flying obsolete PZL P.7a fighters, covering Dęblin and Ułęż airfields.