Complex sentence: The first military uses of aviation involved lighter-than-air balloons; in the Battle of Fleurus in 1794, the French successfully used the observation balloon "l'Entreprenant" to watch Austrian troop movements.
Split into simpler sentences: The first military uses of aviation involved lighter-than-air balloons. During the Battle of Fleurus in 1794, the French successfully used the observation balloon "l'Entreprenant" to watch Austrian troop movements.