Complex sentence: While in route back on the morning of 18 July he noted an oddity: large Allied bomber formations were passing overhead, but instead of heading on to targets in Northern France or Germany they were undertaking a massive bombardment of the German positions at the front.
Split into simpler sentences: While in route back on the morning of 18 July he noted an oddity. Large Allied bomber formations were passing overhead, but instead of heading on to targets in Northern France or Germany they were undertaking a massive bombardment of the German positions at the front.