Complex sentence: However, the War had shown the possibilities and potential for air attack and lessons had been learned, particularly by the British, who had had AA guns in most theatres in action in daylight and used them against night attacks at home.
Split into simpler sentences: However, the War had shown the possibilities and potential for air attack and lessons had been learned. The British had used AA guns in most theatres in daylight, as well as against night attacks at home.