Task: Question Generation
Input (English): On 15 September the Luftwaffe made two large daylight attacks on London along the Thames Estuary, targeting the docks and rail communications in the city. Its hope was to destroy its targets and draw the RAF into defending them, allowing the Luftwaffe to destroy their fighters in large numbers, thereby achieving an air superiority. Large air battles broke out, lasting for most of the day. The first attack merely damaged the rail network for three days, and the second attack failed altogether. The air battle was later commemorated by Battle of Britain Day. The Luftwaffe lost 18 percent of the bombers sent on the operations that day, and failed to gain air superiority.
Output (English): The Luftwaffe lost what percentage of its bombers sent that day?