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NEWS | Nov. 4, 2010

NRL History - RADAR

By Daniel Parry, U.S. Naval Research Laboratory Corporate Communications

In times of war, identifying an approaching enemy can be as critical to defense and counter strategies as often is the element of surprise an advantage to an impending invader. Clearly, throughout history, it is demonstrated that possessing an almost omniscient knowledge toward the motions and actions of a potential adversary certainly detracts from the potency of that surprise.

Adaptation of low tech, yet highly esoteric reconnaissance tactics can reveal the position and movement of an opponent; however, in times prior to electronic means of communication and the ability to observe large tracts of land, and more recently air, this tactic is often constrained to the limitations at which the gathered data could be received and processed, and anything less than surreptitious would greatly compromise the integrity of any collected intelligence.

Possessing the uncanny ability to peer farther out to the horizon than the naked eye can see or unamplified human ear can observe, undetected, gives way to a defensive yet highly passive approach to surveillance and early warning tactic.

Radio Tests Reveal More

In September 1922, nearly eight months prior to the opening of the newly created Naval Research Laboratory, two Navy radio engineers Albert Hoyt Taylor and Leo Clifford Young stationed at the Naval Aircraft Radio Laboratory at Anacostia began to seek new frequencies for radio communication. Building a high-frequency transmitter and portable receiver operating at 60 megahertz (MHz), the two set out to 'field-test' their device by placing the receiver in an automobile and driving it around the grounds of the Anacostia laboratory.

Observing that certain structures and vehicles around the station were interfering, interrupting and even blocking their signal, Taylor and Young decided to transport the receiver across the river to Haines Point, adjacent to the laboratory and unfettered by obstruction. It was during this somewhat whimsical exercise the two were able to more clearly receive and interpret the signals they were observing and confirm an affect first theorized by German physicist, Heinrich Hertz. The idea of using radio transmissions for more than just communication had been a known phenomenon and was even discussed a few months earlier in New York City by inventor Guglielmo Marconi. However, extensive research in this area at the time had not garnered considerable attention.

As Taylor and Young were testing their new equipment across the half-mile stretch of open water, the wooden steamer Dorchester was cruising up the Potomac from Alexandria. As the vessel steamed toward the Anacostia, the researchers took note to the discernable fluctuations and peaks they were observing on their equipment, increasing in intensity as the vessel drew closer. As the ship intercepted, then moved past the transmission path, these signals diminished in intensity and variance.

After somewhat tweaking the efficiency of the signal, the scientists were soon able to more effectively identify approaching vessels along the Potomac, some as far off as three miles. It was soon after this discovery the team truly believed they could further develop their device for practical military use in modernizing the efficiency of enemy detection by Navy warships.

In fact, so emphatic was Taylor, he penned a letter to the Bureau of Engineering explaining in detail their discovery and its practical use in identifying enemy vessels regardless of darkness, fog or other visual inhibitors, particularly for use in safeguarding Navy vessels traveling miles apart on open waters. Unfortunately, neither the Navy nor the Bureau seemed interested, and Taylor and Young in lieu of other demanding priorities shelved the project before being moved slightly down river to the newly commissioned Naval Research Laboratory (NRL) several months later.

At NRL Taylor became chief radio scientists of the Laboratory's Radio Division and Young his top assistant. During the greater portion of the 1920s, the division was tasked with advancing high-frequency radio technology for service to the Navy fleet. This was no remedial task as it involved an almost top to bottom re-engineering of existing systems from antennae to the electron tube to the systems that powered them, developing science-based engineering as the benchmark for future developments at the Lab.

A Phenomena Revisited

As a new decade was approaching, a quarter century of aviation successions, including speed, range and complexity well established the prevalence and sustainability of aircraft for military purpose. As such, developments in aircraft communications and capabilities to improve 'blind flight' and navigation were an integral portion of research being conducted at the Radio Division and within the divisions Aircraft Section under the lead of Carlos B. Mirick.

In June 1930, Young with the assistance of associate engineer Lawrence Hyland — founder of Radio Research Company now known as Bendix Corporation and later the vice president and general manager of Hughes Aircraft — began field testing high-frequency beams used to guide aircraft. After briefly testing new direction-finding equipment at Bolling Field, just north of NRL, Hyland positioned the aircraft to make adjustments to the planes' receiver and antenna and to provide optimal signaling back to equipment stationed at the laboratory. During calibration, aircraft flying overhead were noticeably influencing the signals being read by Young, with greater intensity than signals being observed by the test Vought 02U aircraft still on the ground. Immediately, Young recognized this as an affect he and Taylor experimented with in 1922, but nonetheless impressed by the strength of the reflected signals from aircraft flying overhead.

Under the principles of electromagnetic-wave propagation, radio reflections by aircraft were a known phenomena as Marconi presented in theory earlier, but the severity of the interruption capable of revealing a flying aircraft to a distant receiver had never before been measured. Excited by this discovery Hyland and Young immediately notified Taylor. Realizing that radio detection equipment was as capable of detecting aircraft as it was sea-going vessels and given the airplane was rapidly developing into an important instrument of war, Hyland, Young and Taylor believed they now had significant merit to revive interest in their breakthrough as a device to reveal the location of moving craft not only on water, but in the air and eventually on ground.

In an excerpt from notes by Taylor, he reflects, The Navy was very keenly alert to the significance of the rapid development of air power. We felt sure that they would be interested in any device which could betray the presence, and eventually locate, aircraft as well as ships.

Finding the interference phenomena of considerable value, NRL Assistant Director, Capt. Edgar Oberlin, authorized discretionary funding to perform 'confirming' experiments. For the next few months Hyland and Young, dedicating mostly their spare time, vigorously conducted numerous tests experimenting with varying portable receiver locations and transmitting frequencies up to 65 MHz, each with similar and impressive results, capable of revealing flying aircraft at ever increasing distances.

A Second Chance

By late fall, encouraged by the repeated success of experiments executed by Hyland and Young with assistance from Mirick's Aircraft Section, Taylor was ready to officially inform the Navy Bureau of Engineering of their investigation.

On November 5, 1930 Taylor drafted an 11-page memorandum to the Chief of the Bureau of Engineering providing technical diagrams and detailed reports of the experiments conducted at the Bellevue laboratory. In his letter, Taylor noted:

The Laboratory has at present two definite objectives in this work: the first is to detect the presence of moving objects in the air and on the water, possibly later even on the ground, at such distances that their detection by other well-known methods is difficult or impossible. It may be remarked that the personnel piloting any moving object would probably not know that any observations were being taken upon them. Second, to develop as a byproduct of the principal investigation as a check on the validity of the general theory of the same, a method of measuring the velocity of moving objects at great heights or at considerable distances, or on the surface of the water.

After nearly two months and reminiscent of the cold response received nearly eight years earlier, anticipation of a positive reply from the Bureau again began to wane. Disheartened but certainly not disparaged, then Acting NRL Director, Capt. Edmund D. Almy, launched an endorsement letter at the Bureau, January 1931, stressing the relative importance of Taylor, Young and Hyland's research. In his letter Almy proclaimed with utmost importance the great promise the device held in the detection of surface ships and aircraft and if developed 'would be of the greatest military and navy value for defense against enemy aircraft.'

Soon thereafter, a two-fold response marked 'CONFIDENTIAL' came back from the Bureau, the first addressing Taylor's initial letter in November and the second authorizing further investigation toward the location of enemy vessels and aircraft, assigned under Navy Department problem number W5-2.

The Lean Years

Although the Bureau had conceded the significance of radio detection of aircraft, no funding was specifically allocated toward the project and essentially was an issuance of an unfunded mandate by the Bureau for the Lab to conduct research with available resources and personnel. Undaunted by these proceedings, the team accepted the challenge. Operating under fiscal constraints, Hyland and Young again devoted much of their own time working around existing priority projects and building on recent experiments using continuous-wave methods to detect moving craft.

Through the use of continuous-wave radio transmissions, objects could be detected by sensing the reflection from the target 'beating' with the direct signal from the transmitter through a modulation phenomena appropriately considered the beat, or Doppler, method. Subsequent experiments led to a system devised of an array of fixed transmitters and receivers capable of detecting objects at distances beyond the range of vision, referred to by Taylor as an 'area protections system.' However, the need to widely space transmitters and receivers provided limitations to other than land-based stations, a significant and unappealing hindrance for naval ship applications.

Still recognizing the significance of this technology, Taylor felt the device may more appropriately suit the needs of the Army, and in December 1930 arranged demonstration to officials of the Army Signal Corps, Army Air Corps and Coast Artillery Corps. Among them was Major William Blair, Director of the Signal Corps Laboratories at Fort Monmouth, N.J. Blair, having conducted similar research using shorter radio waves to detect infrared radiation from aircraft was unimpressed by the demonstration and according to accounts, argued with Taylor that the technology provided little benefit toward precisely locating aircraft.

Despite Blair's acrimonious response, Hyland, as did Taylor, remained confident the demonstrated capabilities of their technology held promise. However, Hyland, after experiencing a similar scathing response from the Chief of the Bureau of Engineering, decided to pursue the endeavors of his personal research and resigned from the Lab.

The End to a Beginning

In a somewhat tumultuous period resulting in the transfer of NRL to the Bureau of Engineering in late fall 1931, and a change of command the following spring resulting in Oberlin being replaced by Cmdr. Edmund Almy, the promise of further research again loomed heavy. In lieu of these events, and with continued limited funding and personnel, sporadic work on radio detection continued at the Lab. However, concerns over reports that other laboratories may be close to developing similar technologies prompted a submission for patent, June 1933, to the U.S. Patent Office. Nearly a year and a half later Taylor, Young and Hyland received patent 1,981,884 for a System for Detecting Objects by Radio, November 27, 1934.

Although the applied patent did not directly identify the capability to specifically reveal the location of aircraft or the ability to collocate the receiver and transmitter, a sticking point for naval application, a revived interest was coming from some influential sources and earlier that same year, through the support of the Subcommittee on Naval Appropriations of the House of Representatives, a grant of $100,000 was dedicated to further explore these possibilities.

Receiving the break the scientists had hoped, Taylor immediately positioned Young as head of a special research section at NRL to 'push forward' the ideas of what was to become radio detection and ranging, or radar. Although continuing to expand on the continuous-wave beat method, Young, and his newly assigned assistant Robert Page, a young physicist who had already tenured nearly eight years at NRL, reverted to Young's earlier ionosphere research involving pulse transmissions for the possibility of better achieving target detection and ranging. Taylor responded:

I told Mr. Young that I would be glad to see this tried but warned him that it would be a much more difficult job than getting reflections from the ionosphere. Although the ionosphere was a long distance away, it was a very large and very perfect target, giving strong echoes, whereas the location of an airplane at a similar distance, say 100 miles, would require shorter pulses of very much higher power and new types of receivers. With this understanding we went ahead with the pulse method that was the basis of modern radar.

By December 1934, Young and Page had documented that a pulsed transmitter operating on a 60 MHz cycle with a receiver now located as close as the next building was most capable of detecting aircraft transiting along the Potomac, but difficulties with range detection and other radio anomalies of 'ringing' and 'blocking' remained a few of the many hurdles to overcome.

To assist Page, Taylor assigned another scientist, Robert Guthrie, to help develop a transmitter capable of not only emitting high-frequency short-wave pulses — Guthrie developed the automatic keying mechanism for quick pulsing — but one that could 'listen' for return energy from those pulses.

Guthrie and the others labored for nearly another year, solving problems with equipment availability and technological developments. In what is often the mantra of work at the Lab, Page, performing minor modifications, incorporated many devices and technologies already being developed through other divisions of the Lab. Readily available equipment such as the large curtain array antenna already in use at NRL and off-the-shelf cutting-edge components such as RCA's new high-frequency acorn vacuum tube were just a few items that shaved considerable time and expense from the project.

Following a whirlwind year of development, testing and trials, Page had solved many of the problems associated with earlier tests, including range detection that he could now view on a radial time-sweep cathode-ray tube — later patented as the Plan Position Indicator (PPI). What emerged in spring, 1936, was a somewhat crudely arranged 'soap-box' of mated components, mainly consisting of a 28 MHz transmitter, an A-scope (cathode-ray tube) and use of the aforementioned 200-foot tall array antenna to test the device. Page and Guthrie documented their success:

...the initial test was run on April 28. Success came immediately. Planes flying about randomly were picked up at distances of four kilometers (2-1/2 miles). The echoes were clear and distinct. There was no smearing out or fuzziness, and the received pulses were as sharp as those transmitted. The ringing of the receiver that had marred the test of 18 months earlier was completely gone. The next day, the plate voltage in the transmitter was jumped to 5,000 volts and an aircraft was followed out eight kilometers (5 miles) and back.

Successfully demonstrating to the Lab's Commanding Officer, Capt. Hollis Cooley and other leaders at NRL that a distinct reflection could be obtained from an aircraft 17 miles away, Taylor, Young and the others were poised to give a demonstration of much greater importance and bearing.

In early June, 1936, a demonstration for a group of visiting admirals included Adm. Harold R. Stark, Chief of Naval Operations and Rear Adm. Harold G. Bowen, Chief of the Bureau of Engineering — later to become one of radar' s most enthusiastic supporters — resulted in the problem of radio detection being awarded the necessary funding and the highest possible priority within the Naval Research Laboratory.

In a letter later sent to the Director of NRL, Bowen stated in part, The work should now be centered upon providing for shipboard use...providing in a single device both capable of detection and ranging.

In the months to follow, contributing developments made at NRL — such as the duplexer, or Transmit/Receive switch that made monostatic radar possible — were instrumental in the undeniable success of Navy radar. Test performed aboard the Navy destroyer USS Leary (DD-158) in 1937 and continued technological improvements, revealed an increased transmitter frequency to 200 MHz proved optimal for identifying targets at distances greater than the initial 17 miles. By December 1938, the USS New York (BB-34) became the first active duty battleship to be equipped with the latest in radio detection and ranging, identifying aircraft nearly 50 miles out. By all accounts, and before the close of the decade, radar had at last come into its' own in the Navy, contributing to major Naval victories in battles at the Coral Sea, Midway, and Guadalcanal during World War II.

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