The exact date and origin of the smoking lamp has been lost. However, it probably came into use during the 16th Century when seamen began smoking on board vessels. The smoking lamp was a safety measure. It was devised mainly to keep the fire hazard away from highly combustible woodwork and gunpowder. Most navies established regulations restricting smoking to certain areas. Usually, the lamp was located in the forecastle or the area directly surrounding the galley indicting that smoking was permitted in this area. Even after the invention of matches in the 1830s, the lamp was an item of convenience to the smoker. When particularly hazardous operations or work required that smoking be curtailed, the unlighted lamp relayed the message. "The smoking lamp is lighted" or "the smoking lamp is out' were the expressions indicating that smoking was permitted or forbidden.
The smoking lamp has survived only as a figure of speech. When the officer of the deck says "the smoking lamp is out" before drills, refueling or taking ammunition, that is the Navy's way of saying "cease smoking."
Sound Navigation Ranging. An acronym for underwater echo-ranging equipment, originally for detecting submarines by small warships.