Chicken Rock Lighthouse stands on a treacherous reef off the southern tip of the Calf of Man, built after mariners found that fog often obscured the Calf's older lights, making the reef a serious hazard to shipping. Designed by the engineers David and Thomas Stevenson, the 44-metre granite tower was under construction from 1868 to December 1874, cost more than £64,000, and was first lit on 1 January 1875. A serious fire on 23 December 1960 badly damaged its interior and injured one of the three resident keepers, all of whom were rescued by the Port St Mary lifeboat; the light was automated the following year and has been unmanned ever since. It remains an active aid to navigation operated by the Northern Lighthouse Board, flashing white every five seconds with a range of around 18–21 nautical miles, though the tower itself is not open to visitors.