The buzzing sound of the V-1's pulse jet engine was likened by some to "a motor cycle in bad running order". As it reached its target and dived, the sound of the propulsion unit spluttering and cutting out, followed by an eerie hush before impact, was quite terrifying, though the silence was also a warning to seek shelter (later V-1s were corrected to have the originally intended power dive). At least one business in London advertised how quickly a patron could access a nearby shelter. Despite this, the cloudy and rainy conditions of June and July aided the effectiveness of the weapon, and casualties were high. By late August a million and a half people had left London, and the rate of work production was affected. By the late summer and autumn, however, increasingly effective countermeasures against the V-1 were taken, and people started returning to London.