Searchlights

A searchlight (or spotlight) is an apparatus that combines an extremely luminous source (traditionally a carbon arc lamp) with a mirrored parabolic reflector to project a powerful beam of light of approximately parallel rays in a particular direction, usually constructed so that it can be swiveled about.

The first use of searchlights using carbon arc technology occurred during the Siege of Paris during the Franco-Prussian War. The Royal Navy used searchlights in 1882 to prevent Egyptian forces from staffing artillery batteries at Alexandria. Later that same year, the French and British forces landed troops under searchlights.

By 1907 the value of searchlights had become widely recognized. One recent use was to assist attacks by torpedo boats by dazzling gun crews on the ships being attacked. Other uses included detecting enemy ships at greater distances, as signaling devices, and to assist landing parties. Searchlights were also used by battleships and other capital vessels to locate attacking torpedo boats and were installed on many coastal artillery batteries for aiding night combat. They saw use in the Russo-Japanese War from 1904–05.

Searchlights were installed on most naval capital ships from the late 19th century through WWII, both for tracking small, close-in targets such as torpedo boats, and for engaging enemy units in nighttime gun battles. The Imperial Japanese Navy especially was known for its intensive development of nighttime naval combat tactics and extensive training. The War in the Pacific saw a number of nocturnal engagements fought by searchlight, particularly the Battle of Savo Sound at Guadalcanal. Although searchlights remained in use throughout the war, the newly developed radar proved to be a far more effective locating device, and Japanese radar development lagged far behind that of the US.

...
Wikipedia