Bob's theatre equipment

World War II Searchlight Battery
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 Acoustic location was used from mid-WW1 to the early years of WW2 for the passive detection of aircraft by picking up the noise of the engines. It was rendered obsolete before and during WW2 by the introduction of radar, which was far more effective.
Before Radar, the Sound Locator was the first practical means of detecting enemy airplanes at a distance in the night sky by listening to their engines 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.

1941 Sperry Searchlight and Model M1 Sound Locator

Note the very large hoses going to the operators head. The sound was not electrically amplified to the operator, but acoustically coupled to the operators ears using hoses 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

France

Other Locating Devices that were used in place of the Sound Locator in aiming the Searchlight

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 a mechanical structure 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. It was Radar that eventually made the searchlight battery obsolete in tracking enemy aircraft.

Searchlight Control Station

Once enemy aircraft was located by the Sound Locator, the Control Station was used to aim the searchlight visually 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 signals from the Sound locator was sent to the Searchlight control station using a selsyn type system to send control 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 sync with the same direction and elevation as the locator device tracked enemy aircraft.
The Commander was the third man on this station, and wass 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 was able to spot 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. Using the control station, he would now 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 sound locator are sent to the searchlight. Here, the searchlight operator maintains the light mechanism. He assures that the carbons are burning 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 Commander..
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.

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 the next 60 years as searchlights in the outdoor advertising industry for the promotion of Grand Openings, sales, and special events..

Click HERE to see my restored GE Searchlight ......