Complex sentence: The sole Hungarian loss of the entire conflict was a Fiat fighter which was accidentally shot down by Hungarian artillery; however, the Hungarian Air Force didn't manage to take control of the skies over eastern Slovakia.
Split into simpler sentences: The sole Hungarian losses of the entire conflict was a Fiat fighter, which was accidentally shot down by Hungarian artillery. However, during the operation, the Hungarian Air Force did not manage to take control of the skies of eastern Slovakia.