SCR - 270 radar The SCR - 270 ( Signal Corps Radio model 270 ) was one of the first operational early warning radar s . It was the U . S . Army ' s primary long - distance radar throughout World War II and was deployed around the world . It is also known as the Pearl Harbor Radar , since it was a SCR - 270 set that detected the incoming raid about half an hour before the attack commenced . Two versions were produced , the mobile SCR - 270 , and the fixed SCR - 271 which used the same electronics but used an antenna with somewhat greater resolution . An upgraded version , the SCR - 289 , was also produced , but saw little use . All of the - 270 versions were later replaced by newer microwave units after the cavity magnetron was introduced to the US during the Tizard Mission . The only early warning system of the sort to see action was the AN / CPS - 1 , which was available in late 1944 . Building of the radar . The Signal Corps had been experimenting with some radar concepts as early at the late 1920s , under the direction of Colonel William R . Blair , director of the Signal Corps Laboratories at Fort Monmouth , New Jersey . Although the Army focused primarily on infra - red detection systems ( a popular idea at the time ) , in 1935 work turned to radar again when one of Blair ' s recent arrivals , Roger B . Colton , convinced him to send another engineer to investigate the US Navy ' s CXAM radar project . William D . Hershberger went to see what they had , and returned a positive report . Gaining the support of James B . Allison , the Chief Signal Officer , they managed to gather a small amount of funding and diverted some from other projects . A research team was organized under the direction of civilian engineer Paul E . Watson . By December 1936 Watson ' s group had a working prototype , which they continued to improve . By May 1937 they were able to demonstrate the set , detecting a bomber at night . This demonstration turned out to be particularly convincing by mistake ; the Martin B - 10 bomber had originally been instructed to fly to a known point for the radar to find it , but could not be located at the agreed upon time . The radar operators then searched for the bomber and located it about ten miles ( 16 km ) from its intended position . It was later learned that winds had blown the bomber off course , so what was to be a simple demonstration turned into an example of real - world radar location and tracking . Development of this system continued as the SCR - 268 , which eventually evolved into an excellent short - to - medium range gun laying system . In April 1937 a LtC . Davis , an officer in an Army Air Corps Pursuit Squadron in the Panama Canal Zone ( CZ ) , sent a request for a " Means of Radio Detection of Aircraft " to the US Army ' s Chief Signal Officer ( CSig . ) , bypassing normal channels of command . The SCR - 268 was not really suited to this need , and after its demonstration in May they again received a request for a long - range unit , this time from " Hap " Arnold who wrote to them June 3 , 1937 . Shortly thereafter the Signal Corps became alarmed that their radar work was being observed by German spies , and moved development to Sandy Hook at Fort Hancock , the coast artillery defense site for Lower New York Bay . After the move , work immediately started on the Air Corps request for what was to become known ( in 1940 ) as the " Radio Set SCR - 270 " . Parts of the SCR - 268 were diverted to this new project , delaying the completion of the - 268 . Key to the - 270 ' s operation was the primary water - cooled 8 kW continuous / 100 kW pulsed transmitting tube . Early examples were hand - built , but a contract was let to Westinghouse in October 1938 to provide production versions under the Westinghouse designation " WL - 530 " and the Signal Corps type number " VT - 122 " . A pair of these arrived in January 1939 , and were incorporated into the first SCR - 270 in time to be used in the Army ' s maneuvers that summer . Several improved components followed as the Army offered additional contracts for eventual production . The original - 270 consisted of a four - vehicle package including a K - 30 operations van for the radio equipment and oscilloscope , a K - 31 gasoline - fueled power - generating truck , a K - 22B flatbed trailer , and a K - 32 prime mover . The antenna folding mount was derived from a well - drilling derrick , and was mounted on the trailer for movement . When opened it was tall , mounted on an wide base containing motors for rotating the antenna . The antenna itself consisted of a series of 36 half wave dipole s backed with reflectors , arranged in three bays , each bay with twelve dipoles arranged in a three - high four - wide stack . ( Later production versions of the SCR - 270 used 32 dipoles and reflectors , either eight wide by four high ( fixed ) or four wide by eight high ( mobile ) ) . In use , the antenna was swung by command from the operations van , the angle being read by reading numbers painted on the antenna mount . The radar operated at 106 MHz , using a pulse width from 10 to 25 microseconds , and a pulse repetition frequency of 621 Hz . With a wavelength of about nine feet , the SRC - 270 was comparable to the contemporary Chain Home system being developed in England , but not to the more advanced microwave systems in Germany . This frequency did turn out to be useful , as it is roughly the size of an airplane ' s propeller , and provided strong returns from them depending on the angle . Generally it had an operational range of about , and consistently picked up aircraft at that range . A nine - man field operating crew consisted of a shift chief , two oscilloscope operators , two plotters , two technicians , and two electricians . The declassified US military document " U . S . Radar - - Operational Characteristics of Available Equipment Classified by Tactical Application " gives performance statistics for the SCR - 270 - D , namely " maximum range on a single bomber flying at indicated heights , when set is on a flat sea level site " : Deployment and Incomprehension . The non portable version , the SCR - 271 - A , s / n 1 was delivered to the Canal Zone and began operation in October 1940 at Fort Sherman on the Atlantic end of the Panama Canal . It picked up airliners at in its initial test run . The second set was set up on Fort Grant ' s Tobaga Island on the Pacific end of the Canal by December 1940 , thus giving radar coverage to the vitally important but vulnerable Panama Canal . Westinghouse quickly ramped up production , and produced 100 by the end of 1941 . Operators of sets that were sent to the Panama canal , the Philippines , Hawaii and other strategic locations were all gathered for an air defense school at Mitchel Field , New York in April 1941 . The school was the culmination of efforts began in 1940 , when the War Department created the Air Defense Command headed by Brig . Gen . James E . Chaney . Chaney was tasked by Hap Arnold to collect all information on the British air defense system and transfer the knowledge as quickly as possible to the US military . Air Marshal Dowding , one of the designers of the Ground - controlled interception ( GCI ) air defense system used during the Battle of Britain , was at the school and discussed with the American generals the design and urgency of establishing the Hawaiian system , in particular emphasizing the need for thorough radar site coverage along the coasts . Despite the high level attention and the excellence of the school in training on the use of the SCR - 270 and its integration and coordination with fighter intercepts , the army did not follow through on supporting the junior officers who were trained at this session . Army Major Kenneth Bergquist returned to Hawaii after attending the school intending to set up a coordinated system , but when he arrived he found the local Army leadership was uninterested in the system , and he was reassigned to his former fighter unit . Only when incomprehensible equipment began appearing did the army return Bergquist from his fighter unit and was told his job was to assemble the equipment when it arrived . Assigned the defense of Hawaii , General Walter Short had faint grasp of the weapons and tactics that Army technologists ( led by Hap Arnold ) were aggressively pushing them to adopt . Except in rare cases , there was little interest in assisting or even cooperating with the goal of setting up the air defense system . On his own initiative , Bergquist along with some other motivated junior officers built a makeshift control center without authorization and only by scrounging . The first SR - 270 ' s became functional in July 1941 and by November Bergquist only had a small team established and a set of four SCR - 270 - B ' s stationed around Oahu with one unit in reserve . They were placed on the central north shore ( Haleiwa ) , Opana Point ( northern tip ) , in the northwest at the highest point - Mount Kaala , and one in the southeast corner at Koko Head . However there was no real communications system or reporting chain set up . At one point the operators of one of the sets were instructed to phone in reports from a gas station some distance away . By explicit order by General Short , the radar stations were to only be operated for four hours per day and to shut down by 7AM each day . Although communications were eventually improved , the chain of command was not . Air defense required direct control of assets spread out over disparate units ; anti aircraft guns , radars , and interceptor aircraft were not under a unified command . This had been one of the primary problems identified by Robert Watson - Watt prior to the war , when a demonstration of an early radar system had gone comically wrong even though the radar system itself had worked perfectly . Dowding was well aware of the importance of a unified command , but this knowledge did not result in changes within the Army structure . Use of SCR - 270 radar at Pearl Harbor . Unit s / n 012 was at Opana Point , Hawaii on the morning of the seventh of December 1941 manned by two privates , Elliot and Joseph Lockard . That morning the set was supposed to be shut down , but the soldiers decided to get in additional training time in since the truck scheduled to take them to breakfast was late . At 7 : 02 they detected the Japanese aircraft approaching Oahu at a distance of and Lockard telephoned the information center at Fort Shafter and reported " Large number of planes coming in from the north , three points east " . The operator taking his report passed on the information repeating that the operator emphasized he had never seen anything like it , and it was " an awful big flight . " The report was passed on to an inexperienced and incompletely trained officer who had arrived only a week earlier . He thought they had detected a flight of B - 17 s arriving that morning from the US . There were only six B - 17s in the group , so this did not account for the large size of the plot . The officer had little grasp of the technology , the radar operators were unaware of the B - 17 flight ( nor its size ) , and the B - 17 ' s had no IFF ( Identification friend or foe ) system , nor any alternative procedure for identifying distant friendlies as the British had developed during the Battle of Britain . The raid on Pearl Harbor started 55 minutes later , and signaled the United States ' formal entry into World War II a day later . The radar operators also failed to communicate the northerly bearing of the inbound flight . The US fleet instead was fruitlessly searching to the southwest of Hawaii , believing the attack to have been launched from that direction . In retrospect this may have been fortuitous , since they would have met the same fate as the ships in Pearl Harbor had they attempted to engage the vastly superior Japanese carrier fleet , with enormous casualties . After the Japanese attack , the RAF agreed to send Watson - Watt to the United States to advise the military on air defense technology . In particular Watson - Watt directed attention to the general lack of understanding at all levels of command of the capabilities of radar - with it often being regarded as a freak gadget " producing snap observations on targets which may or may not be aircraft . " General Gordon P . Saville , director of Air Defense at the Army Air Force headquarters referred to the Watson - Watt report as " a damning indictment of our whole warning service " . Use of SCR - 270 radar elsewhere in World War II . In the Philippines , the Far East Air Force did not fare much better than the defending air force at Pearl Harbor . Though FEAF had five SR - 270Bs , only two were functioning on 8 December 1941 , one by a detachment of the 4th Marine Regiment to protect Cavite Naval Base . Even with correct detection of enemy flights from the AAF ' s operational radar at Iba , command disorganization resulted in many of the defending fighters in the Philippines were also caught on the ground and destroyed , as was the largest concentration of B - 17 ' s ( 19 ) outside of the continental US . The Iba set was destroyed in the initial attack on Iba on 8 December . After the first day , the effective striking power of the Far East Air Force had been destroyed , and the fighter strength seriously reduced . The Marine unit was withdrawn to Bataan in January 1942 , where it was successfully employed in conjunction with an SCR - 268 antiaircraft gun - laying radar to provide air warning to a small detachment of P - 40s operating from primitive fields . Key commanders responsible for the defense of installations vulnerable to air attack did not appreciate the need for and capabilities of the air defense assets they had , and how vital radar was to those defenses . The vulnerability was well demonstrated in war games - in particular those of United States Navy Fleet Problem IX that annihilated the locks on the Panama canal , and Fleet Problem XIII , when the Pearl Harbor fleet was destroyed in a mock attack by 150 planes in 1932 . At Midway Island in June 1942 , an SCR - 270 antenna and shack were located at the western end of Sand Island . During the Battle of Midway , this radar was used to warn the island of incoming Japanese air attacks and to successfully direct the fighter interception that followed , but the island ' s radar did not play any significant part in the main carrier - action portion of the battle that followed . SCR - 270s Today . After its use by the military , the Pearl Harbor unit ( s / n 012 ) was loaned to the University of Saskatchewan in Saskatoon ( along with a second unit to the National Research Council in Ottawa ) , who , unaware of its history , used it to image aurora for the first time in 1949 . The technique was published in 1950 in " Nature " , and was a field of active research for some time . In 1990 , having sat derelict for years , they received a phone call informing them of the historical nature of the radar , and requesting it be sent back to the US for preservation . It is now located at the National Electronics Museum near Baltimore . 1942 view of an SCR - 271 at the [ Radar Installation and Maintenance School at Camp Evans ] http : / / www . infoage . org / cs - 12 - 08 - 2005p34 . html , Wall , NJ