November 1899-February 1900

During the Siege of Ladysmith in the Second Boer War, British forces used searchlights to send Morse-coded messages by flashing them onto low clouds, communicating with the besieged garrison at Ladysmith over roughly 30 miles. Boer forces countered by aiming their own searchlights at the same clouds, confusing the coded flashes — an early instance of deliberate signal jamming using light.