Aldis lamps were pioneered by the British [[Royal Navy]] in the late [[19th Century]], and were used up until the end of the [[20th Century]] on board naval vessels. They provided handy, secure communications during periods of [[radio silence]], and were particularly useful for [[convoy]]s operating during the [[Battle of the Atlantic]]. Lamps were normally mounted on the mastheads of vessels; smaller, handheld versions were also used. Power was usually provided by the vessel's emergency [[Electrical generator|generator]], and the lamps were powerful enough to be used during daylight hours. They had a secondary function as simple [[searchlight|spotlights]].