US Navy Searchlight / Signal lamp

USES OF NAVAL SEARCHLIGHTS DURING WWII

This type of signaling and searchlight was used on WW II warships, for example the ‘Destroyer Escort’ (DE). The Destroyer Escort was the United States Navy mid-20th-century classification for a 20-knot (37 km/h; 23 mph) warship designed with the endurance necessary to escort mid-ocean convoys of merchant marine ships.

Ships used a day or night system of sending Morse Code signals via flashing light, using 12" and 24" signal lamps. This was a rapid way of communicating but was rarely used at night for fear that the light would reveal one's position to the enemy. Infrared hooded lenses were used to mask the bright lights of the signal lamps; to limit their visibility.

These lights were designed for signaling, visual search, navigation and even fire control. This light was equipped with a handle on each side of the barrel for left or right handed operators to send visual (light) Morse code. The 24-inch carbon arc was very brilliant and the signals (at night) could be bounced off the cloud cover and around the curvature of the earth. It has been told in visual communicators circles that a Morse signal sent by light has been confirmed (by radar) to have been sent up to a distance of two ships 80 miles apart!

The 24-inch searchlight is a general purpose light and although it may be used for fire control purposes, generally it is used for long range signaling. These searchlights are not equipped with remote control for train and elevation. The light sometimes is equipped with the remote control signal key. This lamp has both the iris and vane type shutter.

Check for a complete story of the General Electric signaling light on the USS Slater: https://ussslater.org/signal-bridge

REQUIREMENTS OF A NAVY SEARCHLIGHT

A Navy searchlight must have a narrow, pencil-like light beam. The light must be non-flickering and of a’bluish white color. It must operate properly from any position, under all weather conditions, and give trouble-free operation over a long period of time. The train and elevation characteristics of most lights are: train through 360°, elevation of 110° to 120°, and depression of 30° to 40°.

THEORY OF CARBON ARC SEARCHLIGHT

When an electric current at a moderate voltage is passed through two carbon rods, considerable heat is developed at the point of contact. Now if the carbon rods are separated a short distance a flaming arc will be drawn out. The act of making contact between the two carbons is necessary to start the arc and is called 'striking the arc'. When contact first occurs, a high current flows through the carbons. The high current produces heat which vaporizes the soft center of the positive carbon. This vapor acts as a conductor for the current as the carbons are drawn apart and will keep the current flowing until the distance between the carbons becomes too great. As the distance between the carbons increases the resistance of the arc circuit increases. The carbon vapor concentrates as a small ball in a depression in the positive carbon. This depression is called the 'crater'. This ball of flaming gas in the crater is intensely luminous and is located at the focus of the reflector. The reflector thus projects the light from the arc crater into a beam of light, just as the reflector in your automobile projects the light from the lamp filament into a light beam. High intensity arcs work on the same principle as low intensity types except that the current is increased and the diameter of the carbon decreased, to obtain a more brilliant and concentrated source of light.

The carbon lamp was designed for operation in series with rheostat (which was mounted below deck) from a d-c source of 105 to 125 volts.

The arc current had to be adjusted for 75 to 80 amperes with 65 to 70 volts across the arc. One set of carbons would burn approximately 1 ž hours.