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Chrysler and radar: the SCR584 radar-mounted anti-aircraft guns

radar setRadar began with work by Dr. A. Hoyt Taylor and Dr. Leo C. Young, government scientists who noticed that radio signals are reflected from steel buildings. They turned their equipment to the Potomac, and were able to track ships moving up and down by tracing interference patterns.

Their 1922 report to the Navy’s Bureau of Engineering was received with enthusiasm. In 1930, they found that they could apply the same principles to aircraft, measuring the time it took for a radio “ping” sent to the ground to return, greatly aiding in low-visibility flight. Unfortunately, from 1926 to 1930, the reports were made public to everyone; the good news is that the British worked independently on it, seeing the potential for discovering invading aircraft (by 1931, American scientists were able to find aircraft fifty miles away). German and Japanese scientists were also working on radar.

dodge radarAt the dawn of World War II, a new British chain of twenty radar stations prevented a major German bombing campaign in 1940. Radar provided an alert of the attack on Pearl Harbor; though R.C. McCloy on the USS Condor had already spotted the planes, no report was sent to naval headquarters. The Army’s radar spotted the attacking planes nearly an hour before the attack started; had the alert been sounded, many American lives might have been saved, not to mention much of the Pacific Fleet.

With the start of the war, the government asked Chrysler to collaborate in both production and engineering — to design, build, and test radar equipment to be used with 90mm anti-aircraft guns. Working under top-secret security, Chrysler finished the project ahead of schedule, and at only 44% of the estimated cost. The patriotic K.T. Keller did not profiteer, and passed along cost savings.

The system was packaged in a single trailer, while the original system had taken seven full trailers, making it much more usable in the field.

The story began in 1942, when two researchers from the National Defense Research Committee joined K.T. Keller to show preliminary sketches of the radar antenna; Mr. Keller said that the paraboloid antenna could not only be made of steel, but could be stamped using auto presses; he also criticized the gearing used to turn the dish, which Chrysler was then building for Canada. As a result, the scientists recommended to the Army that Chrysler provide the entire system, not just the dish. That was approved, and a team was set up, including VP Herman L. Weckler, VP F.J. Lamborn, and C.W. Hirsch, who was made superintendent of the new division. F.W. Slack was responsible for all radar work done within the engineering offices and labs.

The price then was estimated to be $16,451 per unit; less than the goverment’s estimate or that of prime contractor General Electric, who had predicted around $50,000. The actual cost ended up as $9,386. Chrysler engineers were working under the “Three Musketeers” at the time.

George Slider and L. P. Smith were assigned to begin the work. By April 29, 1942, they were at MIT, examining what had been done thus far, which they said was unsatisfactory; it had long trains of spur gears, heavy weight, parts non-interchangeability, and could not achieve close accuracy. A complete re-design was undertaken immediately by Chrysler Engineering staff.

The device had to send out 2,000 10-centimeter microwave radio pulses per second. The particular system produced by Chrysler Corporation was named SCR-584 and was teamed with a heavy anti-aircraft battery of four 90mm guns, a British-invented IFF (identification, friend or foe) unit, a power source, and an M-9 gun director.

The scanning pedestal or antenna mount, officially named Signal Corps Pedestal-MP-61-B, turned at 1,750 revolutions per minute. The plastic-enclosed antenna itself, located at the center of the dish, beamed short wave radio pulses one-millionth of a second in duration at intervals of one twothousandth of a second. The system interpreted the return signal and determined direction, speed, altitude, and course of the target.

Once locked on, the antenna tracked target moves and synchronized the guns. The equipment was designed to cope with aircraft speeds up to 700 miles per hour, up to 60,000 feet, at a target distance of not less than eight miles (Stout, p. 28). A proximity fuse completed the ensemble, since it was effective if triggered within about seventy feet of the target. Gear train accuracy was fundamental to success.

In a matter of months, the whole technology was accelerated. General Electric engineers masterminded the electronic features while Chrysler solved pedestal mounting, dish rotation, and transportation.

The paraboloid reflector dish was engineered at Chrysler out of steel, rather than the aluminum used in the experimental model at the Radiation Laboratory. To withstand winds of up to 60mph and not be tipped over in hurricane winds of 100mph, 6,640 half-inch diameter holes were included in the six-foot dish, saving seventy pounds of scarce steel each (Stout, p. 48).

Chrysler was asked to work out the unsolved mechanical problems of gunlaying short-wave radar, and then develop machines, tools, and processes for production. SCR584 required gearing that would hold to a maximum accumulated backlash of3.375 minutes out of a total 21,600 minutes of measurement. The motor specified turned 3,600 rpm. The dish could turn a maximum of eight times per minute horizontally and less than four times per minute in elevation. Thus reductions were necessary of 472 to 1 and 1,080 to 1 respectively.

So far as was known up to that time, the solution was another Chrysler first: a special planetary-type gear arrangement 2 and 7/16 inches thick and 6 and 7/8 inches in diameter produced a reduction to 120.8 to 1. In turn, this was made to connect with three conventional spur gears with an additional reduction of near 9 to 1, bringing total reduction to 1,080 to 1. The total reduction was completed in a smaller space than the conventional approach of using three spur gears to obtain 8 to 1 reduction. The combination of dual planet gears, in association with a fourth member, a second annulus gear, was unique as far as was known at the time. The parties involved in the project considered this engineering success one of the major contributions to the success of the antenna system.

In addition, the spinner motor required an unlubricated air seal to prevent absorption of short wave impulses by the hollow radio frequency transmission lines. The seal held six pounds of pressure, provided by a small compressor. Friction was minimized by use of Chrysler's Superfinish process, yielding 95 percent optically-flat surfaces on the bellows and seal. The carbon disc (shades of Fluid Drive) between the housing seal and sleeve was also Superfinished.

All wire harnessing was color-coded to distinguish separate circuits, totally interchangeable, machine-tape-bound, and fungus/insect resistant.

Chrysler Engineering designed a special 19 foot, ten-ton semi-trailer that would clear the hatches of Victory ships. They had built-in jacks for accurate leveling. Due to Dodge Main's crowded schedule, the trailers were subcontracted to Fruehauf.

Dodge made up six tool-room models and shipped unit one to Chrysler Engineering for accelerated life-testing on December 4, 1942. System two was placed in General Electric's hands on December 26, 1942. Two more went to the Antiaircraft Board for preliminary trials. Dodge continued to produce while the intensive testing proceeded, completing fifty systems during the testing period.

By August 31, 1943, 610 systems had been shipped. On Columbus Day, 1943, the Army's Signal Corps announced that production would be halted at 1,470 systems plus extras, since the Allies had gained control of the air. This quick-moving program found 132 SCR-584s in the UK before Christmas, 1943.

Dodge Division delivered system #1,470 on January 28, 1944, with 628 additional sets going to the U. S. Marine Corps, coast defense, and spares, for a total of 2,098. By mid-April, 1944, the machine tools and special equipment were moved out of Dodge Main's sixth floor, and the space converted to building B-29 engine pump parts. The SCR-584 residual pilot line equipment was moved to a Defense Plant Corporation warehouse in Indiana.

Operational Results Achieved By SCR-584 Radar-Guided Anti-Aircraft Systems In Combat

The SCR-584 achieved outstanding results in every theater of the war. Using it to direct the hurling of 90mm antiaircraft shells saved Allied lives, both civilian and military. Originally contemplated as a defensive system, it soon proved vital to numerous offensive opportunities.

The initial shipments of SCR-584 systems were sent to North Africa in 1943 for training. When the flawed landing at Anzio in Western Italy turned sour, among the problems was the fact that the enemy successfully jammed the 268 radar. Two complete SCR-584s were rushed into the chaos on February 24, 1944 and dug-in up to their trailer rooftops overnight. The next darkness saw twelve Nazi bombers entering beachhead air space only to lose seven aircraft to the 90mm guns directed by SCR-584. Abruptly, air attacks stopped for a week. A single plane appeared, to test the defenses, only to be destroyed. Ten more systems were emplaced that week, and eliminated the air threat to Anzio.

Twenty SCR-584s were assigned to England's Channel coast to reduce the number of V1 Flying Bombs hitting London. The eighty 90mm guns, using the new proximity-fused shells, destroyed hundreds; on one Sunday, 97 of 101 were shot out of the sky. Less than 10 percent of V-Is reached their targets.

The June 6, 1944 invasion included thirty-nine systems, thwarting Luftwaffe attacks on the beaches.

German forces had penetrated the Ardennes Forest area in 1940, as they outflanked the Maginot Line, forcing France's surrender. The Nazi High Command tried it again in the Battle of the Bulge. As USA forces fought back, George Patton's Third Army had to be pulled out of a committed battle, turned ninety degrees North, and launched toward Bastogne, 100 miles distant. SCR-584s were used in blocking, containment, counter-attack, and resumption of offensive operations. During the first several days, only SCR-584 controlled tactical aircraft could be used, due to terrible weather conditions.

Radar's Role In Gaining The Eventual Victory

Dr. I. A. Getting, Aide to Dr. DuBridge, wrote to K. T. Keller in October, 1945: “Those of us who have worked so closely with you and your engineers feel particularly sad that the closing of our Laboratory will also mean the end of this close association with you. I can honestly say that nowhere during the past five years have I met with a more efficiently administered engineering laboratory or a finer group of fellows than at the Chrysler Corporation.”

Dr. LA. DuBridge, Director, Radiation Laboratory, wrote to K. T. Keller in October, 1945: “No company has cooperated with us in a more patriotic and self-effacing way than the Chrysler Corporation. I have been deeply impressed by the efficiency and speed and ability of both your engineering and your manufacturing people. I am certain that the SCR-584 anti-aircraft radars would not have been completed in time or designed with such reliability had not your group played such an important role.”

Chrysler Corporation helped fill critical needs at a turning point for civilization.

— Dr. David George Briant

(Also see this external page on the SCR584 system) • Chrysler military contributions

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