A Brief History of Marine Navigation Radars [1]


Copyright Ian D Norman 1979

         Radar dates back more than 100 years, to June 1904, when an entrepreneurial 22-year old German engineer demonstrated his "Telemobiloskop"[2], or Fernbewegungseher, to technical representatives from the principal Atlantic shipping companies during a nautical conference held in Rotterdam. It is fitting that this demonstration should be for a marine anti-collision device, and that a "new world" should be demonstrated aboard a ship's tender called Columbus but sadly, the audience was not sufficiently persuaded. Despite the technical innovations, some of which took many decades to re-surface in radar architectures, and some early interest in the device, Christian Huelsmeyer was never able to translate his creation into a marketable implementation. None the less, it is right that this young German engineer be honored as the true inventor[3]of a recognizable radar system.

The Telemobiloskop
Drawing Courtesy of Martin Hollmann

         The shipping lines of the day remained unconvinced, and pursued other approaches to maritime safety: hull-mounted bells provided some measure of proximity warning, and there were numerous sound-location experiments with foghorn and stopwatch. With hindsight, we may wonder at the myopia - literal and figurative - that led to seemingly avoidable tragedies such as the loss of the liner Titanic in 1912, and yet it would be unfair to conclude that radar technology might have prevented early 20th-century disasters. Even in the 1960s, mariners would vilify their radars as collision-assistance devices; so we should not be harsh in judging the rejections of those distant observers. Huelsmeyer's invention was simply far too far ahead of its time for practical purposes, in a world where there were only two accepted kinds of electro-magnetic "signal": lightning, and Morse code. It was to be nearly four decades more before practical implementation of radar, as we know it today, became feasible; and before that could happen, several diverse technologies had to reach maturity. Even so, given the public record, the words of Guglielmo Marconi to the American Institute of Radio Engineers in June 1922 can be seen as informed commentary, rather than the somewhat futuristic prophecy that they may have seemed to his audience:

"It seems to me that it should be possible to design apparatus by means of which a ship could radiate or project a divergent beam of rays in any desired direction which rays, if coming across a metallic object such as another steamer or ship would be reflected back to a receiver screened from the local transmitter on the sending ship and thereby reveal the presence of the other ship in fog or thick weather. One further advantage of such an arrangement would be that it would be able to give warning of presence and bearing of ships even should these ships be un-provided with any kind of radio."[4]


Priming the Pump

         That same year, 1922, German physicist Heinrich Loewy patented what today would be recognized as a "borehole radar" system that, for the first time, used pulsed modulation - another development that would languish for many years before finding its rightful place in modern radar systems. Nonetheless, by the 1920s, radar development was creeping slowly out of the world of science and science fiction, and into the world of engineering implementation:

  • In 1921, nearly two decades before it transformed radar designs, the basic principles of the cavity magnetron were laid out by A.W. Hull, a physicist working for the General Electric Company.
  • The cathode-ray tube, which had been invented several years before Huelsmeyer's Telemobiloskop, by fellow German K.F.Braun, became readily available to engineers around 1922.
  • Around that time, researchers at the Naval Research Laboratory described radio-link interference being caused routinely by a wooden-hulled ferry, the Dorchester, plying its trade on the Potomac River. Similar such observations began to accrue from around the world, particularly in telecommunications industry publications.[5]
  • Other key technologies emerged, in part courtesy of the nascent television industry. In Japan, Doctors Hidetsugu Yagi and Shintaro Uda developed a directional VHF antenna system (1926)[6], and by then the appearance of increasingly high-frequency transmission devices was becoming routine. One, in particular, deserves mention: in 1928, Japanese engineering graduate Kinjiro Okabe created an adaptation of Hull's earlier design; this new split-anode magnetron rekindled interest in the device as a potential high-power RF source, and Okabe had unwittingly spurred radar development, although his goal had been to develop point-to-point inter-island communications.[7]

The pace of scientific discovery and engineering development accelerated in the 1930s:

  • In the Soviet Union, Orwellian bureaucracy slowed but could not stop the creation of an early 3-dimensional radar system, which almost made it into production before hostilities intervened.
  • In France, experiments by Dr. Henri Gutton led to the development of an anti-collision radar that was capable of detecting coastlines at distances of up to 12 kilometers; this system was installed in the liner SS  Normandie  in 1935, to which vessel goes the honor not only of being possibly the greatest ocean liner of the 20th century, but also the first ship ever to be fitted with an operating anti-collision radar. Sadly, the ship was gutted by fire and capsized in New York Harbor while being converted for troop-carrying duty as the USS Lafayette, years after Gutton's early technology was removed after her maiden voyage.
  • In Germany, a naval research laboratory had, by 1935, developed a system capable of detecting ships at ranges similar to the Huelsmeyer and Gutton systems[8]. This led very quickly to the installation of a Funkmessgeraet, or radio-measurement equipment, on the pocket-battleship Graf Spee. To this vessel goes the honor of being the first to sail with a pulsed radar system, when in 1937 it provided moral support to Nationalist forces during the Spanish Civil War; the earlier French system had relied on non-pulsed detection methods. This radar system also was lost, off Montevideo in 1939, when the ship was scuttled to avoid capture.

         Despite these developments, the focus in the USA, Germany and Great Britain, as in the Soviet Union, was much more on the detection of aircraft than of ships. The result of this focus was undoubtedly pivotal to the outcome of the impending conflict, and is worth study by historian and technologist alike, but it is beyond the scope of this brief marine radar history.

Accelerating to Success

         At the outbreak of conflict in Europe, in 1939, radar for ships was largely impractical, despite the recent French and German developments:

  • Systems required separate transmitter and receiver antennas, and antenna movement - even when it was possible - was a laborious process.
  • The operating wavelengths were comparatively long, necessitating large antennas that represented too much top-hamper for all but the largest vessels. Even so, most radiation patterns were more akin to floodlight illumination than to pencil beams, and direction-finding often involved "tuning" a receiver-antenna array with goniometers[9] to compute a direction to the target.
  • Available transmitter power was inadequate for the needs of radar, which must rely on relatively minute levels of reflected energy for target detection.
  • Target detection itself was a manual operation, with those weak reflections causing deflection of a swept time-base on a cathode-ray tube; intensively demanding of the operator, with a low probability of detection.

         Waiting in the wings for the new decade were several critical developments that were to transform radar into something that any modern-day user would recognize:

  • Developments in magnetron design had continued throughout the 1930s, with the most recent (1938) US patent, for a multi-cavity magnetron[10], going to physicist Hans Hollman of Germany, a scientist viewed with pride by his nation today as the father of modern radar; but history records most favorably the work of two British physicists, John Randall and Harry Boot. They had been assigned to explore the viability of multi-cavity magnetron devices, as part of a broad initiative in Britain to find viable high-power sources; and in 1940 they achieved the apparently unattainable: 10-centimeter wavelengths, incredibly short for that time, and power output[11] beyond the wildest hopes of would-be radar designers. With that, the culmination of decades'-worth of published research from many countries, mobile radars became an engineering feasibility: antennas might become small, pencil beams might be formed, and extravagant power might bathe the seascape. For some idea of its import, we need only consider the development of airborne intercept radars: a radar-equipped interceptor of 1939 required a 6-meter antenna with which it could barely become airborne, and could only occasionally detect targets up to 5 kilometers away; by 1941, a successor system had a 1.5 meter antenna, and routinely detected targets up to 15 kilometers distant.
  • In 1940, an air force research laboratory in southern England implemented a protection device that allowed transmitters and receivers to share a common antenna, possibly exploiting knowledge brought by two scientists fleeing from the Netherlands ahead of occupation forces. Now, although the development was intended for airborne radars, smaller ships might potentially afford the top-hamper that radar antennas represented, making it possible to deploy radars widely around the Allied fleets; and receivers, unburdened of the need to screen out leakage from their associated transmitters, could become much more sensitive.
  • In the same year, and at the same laboratory[12], a different team conceived of a new method for operating cathode-ray tubes, a method which involved deflecting a ray trace from the center rather than from one edge, slaving the angle of deflection to the pointing angle of an antenna, and intensity-modulating - rather than merely distorting - the trace when echoes were detected. With this development, the Plan-Position Indicator or PPI was born.
  • Last, but by no means the least of the developments in 1940, a new method of rotating antennas was developed. Until then, British ground-based radars had been turned mechanically, by uniformed female personnel pedaling furiously. The motor drive relieved them of this onerous chore, although radars rotated in this way continued in service elsewhere, perhaps until the 1960s.

         Radar had come of age, after a sometimes-painful 36-year gestation period, and was to take an increasingly diverse range of forms in the following years. The first marine deployment of a latter-day system, a pulsed radar design with a motor-driven antenna, magnetron transmitter and PPI display, was onboard the already-elderly destroyer USS Semmes [13]  in 1941. By then, the British nickname for the device, RDF or Radio Direction Finding, had been dropped in favor of the United States Navy's cover term for this war-winning technology: RADAR.

1942-Vintage US Navy 10-cm "SG" Radar,
as Installed in USS Semmes

          Many operational lessons were learned in the war years, in how the technology could be used to meet military needs, the limits of its reliability, and how to ameliorate its many quirks and shortcomings. Some of those lessons translated into new development, such as meteorological radars designed to sense weather-related effects rather than to filter them away; antenna design; magnetron improvements (by war's end, the US and its allies had mass-produced over a million cavity-magnetron devices); PPI enhancements; tracking facilities, and so on.

         Mostly, from a marine safety perspective, 1945 found a military workforce skilled in tuning and exploiting radar information; but the onset of peace led to a severe hemorrhaging of this expertise, as the workforce progressively demobilized. Engineering development languished, too, as governments found more pressing needs to be addressed. But eventually, commercial pressures exerted themselves, and slowly radar became a feature of worldwide mercantile fleets. Possibly the most compelling step in this process came in 1951 when, frustrated by their difficulties in operating port facilities efficiently in poor weather, and sorely in need of the US aid being shipped eastward under the Marshall Aid Plan, European nations began testing radar technology for vessel traffic management, first in their ports, and then - as confidence grew - in their seaways. Thus began another new age of radar.

The Modern Era

         This new age, the civil use of marine radar, had many lessons to learn, lessons that had been learned by the military but had not been passed on. Attempts at creating berthing radars with short wavelengths, for instance, failed as they were bound to fail, thwarted by the very same weather conditions that had spurred the desire to apply radar solutions. Many near-collisions occurred, as mariners wrestled with how best to adjust threshold controls - and unwittingly desensitized their equipment; and there are countless tales of misinterpretation, as novice radar users attempted to grasp differences between the wax-pencil traces on their displays and the true motion of the target being tracked. It's hardly surprising that radar earned its wry description, as a collision-assistance device. Nonetheless, the cat was out of the bag.

         By 1961, the fledgling International Maritime Organization had recognized radar's potential rôle as an aid to safety and navigation, and began to prescribe regulations for its proper use. At the same time, the International Telecommunications Union, faced with the challenge of ever-thickening electronic "smog", began tightening the rules on the use of the electro-magnetic spectrum, distinguishing between "radio navigation" and "radio-determination" usage and mandating whereabouts within the usable radio spectrum these services might operate. Around the same time, the transistor began appearing in mass-production volumes, proving a pivotal development in the design of marine radars - as, indeed, it influences all modern electronics[14], through mass miniaturization and reliability.

         The radar designs of the 1960s were large and heavy, often requiring dedicated cooling services - some magnetron designs were water-cooled - and invariably necessitating that much of the equipment be below mast-head. Ships' radio officers required extensive training and logistic support for radar maintenance, and down-time was almost-intolerably frequent. Progressively, however, diode- and triode-tubes were replaced by transistors and then transistor-based microprocessors, designs became increasingly compact and reliable, and much of the hardware migrated upwards, towards antenna systems, thereby yielding greater sensitivity and performance.

         By the late 1980s, manufacturers were beginning to market marine radars with only the display system below mast-head, and maintenance-training had begun to fade from the apprentice marine radio officer's curriculum. Today, systems have become so compact and reliable that they require very little care and feeding, and are sufficiently inexpensive (some as little as $1500, in 2011 prices) that sometimes it may cost less to replace than to repair.

         The transistor has wrought many other, more dramatic changes in marine radars, especially those related to processing and display of target information. Nowadays, the once-ubiquitous fluorescent-wax pencil is almost impossible to find, and the jumble of cleaning materials that once were essential to a clear, un-smirched display have largely vanished, too. It is commonplace for new systems to:

perform target detection automatically,
generate and link tracking symbols,
calculate true motion from successive observation and to highlight potential risk situations,
facilitate watch-officers' "what if" maneuver conjectures,
alert to new or changed situations,
sound alarms,
detect sea birds for the commercial fisherman

   - a host of actions, enabled by digital processing and programmed logic. Conversely, it has become extremely rare for a radar display to depict only radar information: even the humblest designs, for recreational vessels, will likely include a position derived from a global position system such as the US GPS, the European Galileo or the Chinese Compass. Virtually all modern display systems include the capacity to fuse radar data with electronic charts and navigational planning data, and increasingly with other sensors: echo-sounders and fish-finding sonar, speed-log data, weather information from broadcast satellite weather services, navigational information from adjacent vessels, infra-red and low-light scanners, laser-based ranging sensors for docking, engine and rudder information; and so on. The most recent trend is the emergence of the so-called "black box" radar, a modular architecture in which the purchaser interfaces the sensor with pre-existing displays, rather than purchasing yet another visual display unit.

         The modern vessel's bridge is progressively becoming a "glass cockpit", shared displays presenting the watch officer with a crisper picture of the prevailing environment than even the most clairvoyant commander might have begged for his Combat Information Center in radar's early days. 

References & Footnotes

[1] Derived from 'A Short History of Radar at Sea', © Ian D Norman 1979. 'Radar' ='Radio Detection And Ranging.'
[2] The '-skop' fragment of this compound noun refers to 'range' or field-of-view, and not to a display device. The first public demonstration of the Telemobiloskop occurred in a hotel in Cologne, Germany, in May 1904, some 36 years ahead of today's radar "scope."
[3] Many other claimants appeared, most notably in the 1940s; but the patent records of Germany, as well as Belgium, Britain, Denmark and the USA, bear silent and unimpeachable witness.
[4] "The Telemobiloscope, an Edwardian radar", V. J. Phillips, Wireless World, July 1978. Marconi was well aware of the Telemobiloskop, and anecdotal history implies that he may have willfully obstructed its development.
[5] What might be termed "parasitic radar" was slowly shouldering itself into public view, independently of any conscious human pursuit.
[6] Ironically, a Yagi-Uda antenna was used in the fuze mechanism to trigger aerial detonation of the nuclear weapons used against Japan, in 1945. "Scanning the Past", Proceedings of the IEEE Vol. 81, No. 6, June 1993.
[7] Japanese military research organizations would employ Okabe as a civilian advisor on radar and communications technologies during the following war.
[8] The developers were reputedly greatly surprised when their patent application was rejected by the German patent office, on the grounds that it was little more than a reworking of the earlier patent granted to Hülsmeyer, of whom seemingly they had never heard. History is cruel to the inattentive.
[9] This required adjusting a delay between adjacent antenna elements, from which a direction of arrival might be deduced; multiple, widely-separated targets likely caused mayhem for the radar operator!
[10] This device was granted a German patent in 1935. Bureaucracy can be slow.
[11] Their first device generated about 6 kilowatts (kW) of RF power. The most powerful magnetron prior to this had generated about 10 watts.
[12] Post-war anecdotes indicate that the creative work was done both in the laboratory and in a nearby tavern, the world's problems being solved over many a liquid lunch. This worthy establishment, properly known as "The Square And Compass" but known fondly by the laboratory staff as "The Sine and Cosine," was hosted by the auspiciously-named Horatio Nelson Baron.
[13] A fate different from her forebears awaited; Semmes was scrapped in 1947 at the ripe old age of 29, after wartime service as a trials vessel and long after her first radar was jettisoned.
[14] This humble device has been labeled among the greatest inventions of the modern world, as significant as the printing-press. A modern microprocessor may have over 400 million transistors.