World War II  Searchlight History

Few people realize that all 60 inch Carbon Arc Searchlights are all 60 years old or older.  Ten thousand were made, mostly ending up in Europe for WWII. One guess puts the surviving number at about 2500 worldwide.   They were built by the General Electric  and Sperry Gyroscope  for the U.S. Military as Anti-Aircraft Searchlight Units. Their original purpose was to aide World War II
anti-aircraft gunnery crews in spotting enemy aircraft during night-time air attacks.  These lights
have not been built since 1944.  They no longer had a military use after the war having been replaced by the invention of radar.

The Very first Carbon Arc Searchlight
The very first Searchlight ever built  was made by General Electric.  It first appeared in Chicago at the World's Columbian Exposition of 1893.  After this Exposition, Thaddeus Lowe, a California entrepreneur who owned Mt Lowe, bought the light for his popular mountain top resort, and tourist observation post in the mountains above Pasadena California.  How he raised the money to buy it is unclear , but some how or an other the U.S.  Army got involved, and might of footed part of the bill.  And why not, the 6,000,000 candlepower searchlight, built by General Electric could prove vital in coastal defense an other areas of warfare.   When it arrived in Pasadena in August of 1894 it was placed on its temporary home at the top of Echo Mt. at Lowe's own, "White City". It was first lit at the top of Mt. Lowe on January 1910.    What happened to the searchlight in later years is unclear.  I have been told what remains of this light is in storage somewhere in Pasadena Ca.  Learn more about Mt. Lowe and the searchlight HERE.
Source: Taken in part from an article in the Lighthouse Digest February, 2001  Mt. Lowe's Search Light The Most Powerful in the World.

Photo Courtesy : Jake Brouwer

The Largest Carbon Arc Searchlight:

 The largest Carbon arc searchlight ever built was built was an 80 inch searchlight build in 1903 by General Electric.  It was installed on top of the City Hall of University City near St Louis for the "1904 St. Louis Worlds Fair".  This light boasts an output of 1 billion Candle power.  It was recently restored in 2004 for a Centennial Celebration.
Weighing in at eight tons, the seven-foot tall searchlight rises through the roof of City Hall on an electric elevator. E. G. Lewis, founder of University City and later its first mayor, installed the searchlight at the top of what was then the Women’s Magazine Building. It made its debut on opening night of the World’s Fair, April 30, 1904, from its perch 135 feet above street level. It was said that on a clear night, the 2 billion candlepower searchlight could be seen as far away as Chicago and Kansas City.

60" Carbon Arc Searchlight Facts:
Searchlights were produced from 1932 to 1944 by Sperry and General Electric at a cost of $60,000 each! 
Light Source: 1 inch Carbon Arc (no light bulb!)
Candle Power: 800,000,000 (800 million)
Effective Beam length: 5.6 miles
Effective Beam visibility: 28~35 miles
Glass Weight Totals: 75 lbs
Brass Rhodium Coated Mirror: 180 lbs

Generator Power: 15 KWV nominal - 16.7 KWV max. (15,000~16,700 watts D.C.)
Powered By: In line 6 cyl. "Hercules" Flathead Engine
Generator Engine Fuel: Gasoline (can also be run using Kerosene or Gasohol) 26 gallons
Generator Fuel Consumption: 2.6 Gal per hour
Combined Weight: 6,000 pounds (3 tons, or the weight of 3 Ford Mustangs combined!)

Light Source
The Beam is made by 2 carbon rods, one positive and one negative, arching within the focal point of a 60 inch
parabolic mirror. The actual light source is only 1 inch in diameter before it is magnified by the mirror..  As the rods "burn" they are automatically fed into the arc. The rods last approximately 2 hours and then are replaced. The flame that is visible during the lights operation, is not actually the source of the light, rather, it is a by-product, produced as a result of the electricity arching between the 2 rods. The flame is the rod slowly burning away as it is fed into the light. The arc draws 150 amps continuously at 78 volts DC, and burns at over 3,000 degrees Fahrenheit. The power is supplied by the D.C. generator which was designed specifically for this purpose.

Accessories and how they all
worked together!

An Anti-Aircraft Searchlight Battery was used for the detection, location and illumination of enemy aircraft during darkness enabling Gun Batteries to fire at enemy aircraft efficiently.  The battery was made up of 2 transport trucks, Searchlight, Control Station, Sound Locator, Power plant, and interconnecting cables.

It took a team of 12 men to operate ONE Searchlight Battery!

The Sound Locator Squad was made up of 5 men
Chief of Section (Sergeant)
Azimuth Listener
Elevation Listener
Acoustic Correction Operator
Telephone Operator

The Searchlight Squad was made up of 7 men
Searchlight Commander ( Corporal)
Azimuth Controller
Elevation Controller
Light operator
Power Plant Operator /Truck Driver
Truck Driver
A Basic (spare man)

The Sound Locator

Before Radar, the first practical means of detecting airplanes at a distance in the night sky was by listening to their engine noise with the aid of listening sound horns. The size of the horns served to gather in and acoustically amplify more of the sound and thus increased the range of detection. The spacing of the horns aided the operator's binaural sense in determining the plane's direction.
Below is a photo of one of the last Sound Locator unit that was used during World War II, Model M-1, made by Sperry Corp. The azimuth operator listened to the left and right horn for direction information, and the elevation operator listened to the top and bottom horns for elevation information.  There was also the Acoustic Correction Operator to compensate for sound delay.  As the operators pointed this large hearing device, their direction and elevation movement would generate  electric signals that would be sent to the searchlight control station,  or to the searchlight directly, using a  selsyn system.  During the start of the war, radar was invented and during the war eventually replaced these sound locators to detect aircraft.  When replaced by radar, Sound Locators were then placed in the field as decoys to let the enemy think sound locators were still being used instead of radar.
Sound locators were built by the Sperry Corp. Sperry's wartime contribution was significant. By1943, the company was manufacturing 300 different products for the war effort, two-thirds of which had been developed within the prior ten years.  The sound locator picks up approaching planes before they are visible and determines their exact position, speed, and direction of flight. Simultaneously, the anti-aircraft director, functioning as a computing mechanism, determines the direction, elevation, and setting required to aim the anti-aircraft gun at the approaching airplane and transmits this information automatically to the guns through a remote control system.
Not only did Sperry invent and manufacture these products during the six-year period from 1939 to 1945, Sperry also ran in-house schools where they housed, fed, and trained over 77,000 military and naval personnel in the use and maintenance of Sperry equipment.

Note the very large hoses going to the operators heads. The sound was not electrically amplified, but acoustically coupled to the operators ears like the stethoscope a doctor uses to listen to your heart.

Below are early 1927-1935-model sound locators . They had 4 horns.   One operator listened to the left and right horn for direction information, and the other operator listened to the top and bottom horns for elevation information.  These units were used since the early 20's

Below are Sound Locators used by other Countries

                                                        Japan                                        England                                   Germany


Heat Detecting Locator

Heat detectors were used to locate enemy aircraft. Looking like a searchlight, this device swept the sky to detect heat from the engines of enemy aircraft.  Thermopiles and control equipment designed by the Signal Corps Laboratories were mounted in  mechanical structures previously built by the General Electric Company on an Engineer Contract. As operated in 1937, the heat  detector received directional data from the radio equipment  and in turn controlled the pointing of a searchlight.

Radar Locator

As the war, and technology progressed,  the new invention of Radar was added to the list of Locator devices used to point the Searchlight to light up enemy aircraft targets.

Searchlight Control Station

This control station was operated by three men.  It could manually aim the searchlight by remote control. The control station was placed several hundred feet away the searchlight in order to see illuminated aircraft better.  The beam was so bright, if you were right next to the searchlight, you would mostly see illuminated atmosphere in the path of the beam.  This distance was also  for safety. You do not want to be next to a searchlight pointed into the sky full of enemy aircraft as these lights also make great targets.

Electric Selsyn  signals from the Sound, Heat, or Radar locators were sent to the Searchlight control station using a selsyn type system to send signals to the zero locator meters that were on top of the station.   Two of the operators, looking at zero locator meters, one for direction and one for elevation, would watch these meters and keep the meters on a zero reading using hand cranks on the side of the unit. Keeping these meters set at zero  would keep the control station and searchlight in the same direction and elevation as the locator device tracked enemy aircraft.
The third man on this station was the observer.  With the observers head in a harness, and using binoculars attached to the station, as the station was aimed by the other two men following the zero locator meters, the observer was forced to visually look at the same direction and elevation that the locators were aimed at.  Once the observer spotted the enemy aircraft, he would then take full control of the station using the crank controls located in front of him. These controls were directly connected to the same crank controls the two other operators used to aim the station.  This would send Selsyn signals to the searchlight so it would track the observers actions.  The observer could also throw a switch on the control station so the searchlight could take Selsyn control signal directly from the locator device whether it be a sound, heat, or radar locator.

The Searchlight

Finally, the signals from the control station or location sensing device are sent to the searchlight. Here, the searchlight operator maintains the light mechanism and generator. This generator powers all the other equipment as well as the searchlight.  The operator assures that the carbons will burn correctly, the beam is focused, and is the one who throws the switch to start the arc burning on command given by the control station operator.
In the event of a communication failure, he may also control the aim of the light by hand control.  This is done by using a long, 10 foot rod with a wheel on the end.  With this rod he can walk the searchlight in the direction he wants and turn the wheel to the elevation he wants. The 10 foot distance give him a better view of the object away from the beam path as well as a safer distance from the light in the event of an attack.

After the War
After W.W. II, Radar had taken over the job the searchlight once had in spotting and tracking enemy planes.  The military kept some units that were used as spotlights through the Korean War, but most of the lights were scrapped, and sold to the public to be used for more than 60 years as searchlights in the outdoor advertising industry for the promotion of Grand Openings, sales, and special events.

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