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

From an article by Dr. David George Briant in the WPC News

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In the early 1920s, two government scientists, Dr. A. Hoyt Taylor and Dr. Leo C. Young, figured out how track ships moving up the Potomac River by tracing the patterns in radio waves reflected off their steel bodies.

In 1930, they applied the same principles to aircraft, measuring the time it took for a radio "ping" sent to the ground to return, aiding low-visibility flight.

Unfortunately, from 1926 to 1930, the reports were made public; while there was some benefit (the British worked independently on it, seeing the potential for discovering invading aircraft), German and Japanese scientists were also working on radar.

By 1931, American scientists were able to find aircraft fifty miles away. In 1940, a new chain of twenty British radar stations which prevented a major German bombing campaign. Radar also 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 U.S. Army's radar spotted the planes nearly an hour before the attack started, but without any procedures to pass on their findings, and with fairly untrained operators, nothing was done. Had the alert been sounded, many American lives might have been saved, not to mention much of the Pacific Fleet.

Chrysler entered the story in 1942, when two researchers from the National Defense Research Committee joined then-president K.T. Keller to show sketches of the radar antenna; Mr. Keller said that it could be made of steel, rather than scarce aluminum, and stamped using auto presses, rather than painstakingly machined. An engineer, 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. 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.

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The price for the system, created to guide anti-aircraft guns, 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, and finished ahead of schedule. The patriotic K.T. Keller did not profiteer, and passed along cost savings.

Chrysler's system was packaged in a single trailer, while the original setup had taken seven full trailers.

By April 29, 1942, Chrysler's George Slider and L. P. Smith were at MIT, examining the prototype; they said it had long trains of spur gears, heavy weight, parts non-interchangeability, and could not achieve close accuracy. Gear train accuracy was fundamental to success, so a complete re-design was undertaken immediately by the Chrysler Engineering staff.

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The device had to send out 2,000 10-centimeter microwave radio pulses per second. The 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 was officially named Signal Corps Pedestal-MP-61-B. The plastic-enclosed antenna, at the center of the dish, beamed short wave radio pulses one-millionth of a second in duration at intervals of a two-thousandth of a second. The system determined direction, speed, altitude, and course of the target from the return signal. To withstand winds of up to 60mph (and not be tipped over in hurricane winds of 100mph), 6,640 half-inch holes were included in the six-foot dish, saving seventy pounds of scarce steel per unit (Stout, p. 48).

Once locked on, the antenna tracked target moved 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 eight miles (Stout, p. 28). A proximity fuse in the ammunition was effective if triggered within about seventy feet of the target.

In a matter of months, the whole technology was accelerated. General Electric worked on the electronics while Chrysler solved mechanical and production issues.

SCR584 required gearing that would hold to a maximum accumulated backlash of 3.375 minutes out of a total 21,600 minutes of measurement. The motor turned at 3,600 rpm; the dish could turn eight times per minute horizontally and around four times per minute in elevation. Thus reductions were necessary of 472 to 1 and 1,080 to 1, respectively.

The solution was another Chrysler first: a planetary gear arrangement 2 and 7/16 inches thick and 6 and 7/8 inches in diameter produced a reduction to 120.8 to 1, and connected with three conventional spur gears with an additional reduction of near 9 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 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 designed a 19 foot, ten-ton semi-trailer that would clear the hatches of Victory ships, with built-in jacks for accurate leveling. Due to Dodge Main's crowded schedule, the trailers were subcontracted to Fruehauf.

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Dodge made up six tool-room models and shipped unit one to Chrysler Engineering for 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. The same year, the 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 the end of 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 for 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 was 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, saving many Allied lives, both civilian and military. Originally a defensive system, it soon proved vital to offensives.

The first 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 of them to the 90mm guns directed by SCR-584. 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 guns, using new proximity-fused shells, destroyed hundreds; on one Sunday, 97 of 101 were shot out of the sky. Less than 10% 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 to block, contain, counter-attack, and resume the offensive. 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 Chrysler military contributions)

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