Complex sentence: Thomson Brandt calculated and demonstrated in trials that 12 to 18 bombs were required to effectively cut an airfield runway, the number depended on the sighting system of the delivery aircraft and on the size of the target.
Split into simpler sentences: Thomson Brandt calculated that between 12 and 18 bombs were necessary to effectively cut an airfield runway, this was later demonstrated in tests. The number of bombs depended both on the sighting system of the delivery aircraft and on the size of the target.