At just after 8.30pm the alert was sounded and at 8.39 the attack started. First came a group of Heinkel III bombers flying at between 9,900 and 11,500 feet. Included in the load of bombs that they dropped were 34 delayed action high-explosive ones. The pathfinder force, who should have arrived first and dropped flares to light the target, arrived at 8.41pm, flying at an altitude of 19,000 feet. Their shower of flares was followed by 12,500 incendiaries and other high-explosive bombs.