The British followed the main raids and were aware of all the approaching aircraft, save for the low-altitude 9 Staffel. The radar station near Dover began reporting a build-up over the Pas-de-Calais area. This activity increased until 12:45 when six separate concentrations were reported. The plotters estimated the strength of the force as 350 aircraft, one-third more than the actual size.
At RAF Uxbridge, AOC No. 11 Group RAF Keith Park and his controllers directed No. 501 Squadron RAF and its 12 Hawker Hurricanes, already in the air, to Canterbury at 20,000 feet. They had been on their way back to RAF Gravesend having spent most of the morning on patrol operating from RAF Hawkinge near Folkestone. Within minutes eight more Squadrons were dispatched to meet them; two from Kenley, two from Biggin Hill and one each from North Weald, Martlesham, Heath, Manston and Rochford.
Within a short time the fighters assigned to engage were all airborne. Five Squadrons; No. 17, No. 54, No. 56, No. 65, and 501 with 17 Supermarine Spitfires and 36 Hurricanes were moving to patrol the Canterbury-Margate line to block any attack on the Thames Estuary ports of the airfields to the north of it. Four Squadrons; No. 32, No. 64, No. 601, and No. 615, with 23 Spitfires and 27 Hurricanes went into position above Kenley and Biggin Hill. A total of 97 RAF fighters were to meet the attack.
Park did not send all of his forces aloft, and he held a reserve. Three Squadrons at RAF Tangmere were kept and made ready to meet more attacks from the south. Six more were in reserve to meet a possible follow-up to the coming raid.
Quo Fata Vocant-Whither the Fates call