Complex sentence: Later in the war, a "night roundel" was used for night flying aircraft, especially Handley Page O/400 heavy bombers, which dispensed with the conspicuous white circle of the "day" marking.
Split into simpler sentences: Later in the war, a "night roundel" was used for night flying aircraft--especially the Handley Page O/400 heavy bombers. This dispensed with the (very conspicuous) white circle of the "day" marking.