After their major exertions on 15 and 16 August the Germans paused to recover on 17 August but returned in force the next day with 750 sorties. Just after midday the heaviest formations of enemy aircraft yet seen during the battle stimulated 11 Group to bring every serviceable aircraft it had to readiness. Two consecutive raids hit Biggin Hill before the sector station at Kenley came under heavy attack from co-ordinated waves at low and medium level. Both formations were intercepted but severe damage was caused as all ten hangars and twelve aircraft, including ten Hurricanes, were destroyed. The runways were heavily cratered, although still usable, and the communications network was so badly affected that the Sector Operations Room had to be moved to an emergency location off the airfield. For the rest of the battle, Kenley could accommodate only two squadrons instead of three. At Croydon one of the previously undamaged hangars was hit and West Malling was also bombed. Shortly after 2.00pm four separate formations approached the Isle of Wight from the south. The most significant target was Poling radar station which was put out of action for the rest of the month. Its loss was serious, but it was the last to be heavily attacked during the battle. At 5pm another large-scale attack converged on Kent, but an attempt to bomb Croydon by some aircraft was blocked by fighters from North Weald and Hornchurch. The losses of Junkers 87 "Stuka" dive bombers during the day were so severe that this type of aircraft was withdrawn from the main battle by the Germans, apart from a few later isolated sorties. It has been asserted that 18 August was the "hardest day" of the Battle of Britain. However, the intensity of air activity was greater on 15 and 16 August and the number of Fighter Command aircraft in combat was exceeded on at least half a dozen other days.