SCR-270
The SCR-270 was one of the first operational early-warning radars. 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 an SCR-270 set that detected the incoming raid about 45 minutes before the 7 December 1941, attack on Pearl Harbor 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. The -270 versions were eventually replaced by newer microwave units based on cavity magnetron that was introduced to the US during the Tizard Mission. The only early warning system of the sort to see action in World War II was the AN/CPS-1, which was available in mid-1944, in time for D-Day.
Building of the radar
The Signal Corps had been experimenting with some radar concepts as early as 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, 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 3 meter prototype, which detected a unlighted bomber at night, in a demonstration to the Secretary of War. Then in 1938, the 1.5 meter prototype was demonstrated to Hap Arnold. 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 far 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, sent a request for a "Means of Radio Detection of Aircraft" to the US Army's Chief Signal Officer, 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 3 June 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 as the "Radio Set SCR-270". Parts of the SCR-268 were diverted to this new project, delaying the completion of the -268.
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 Taboga 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 begun 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 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. 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 U.S. Army structure.
SCR-270 radars on Hawaii prior to the Pearl Harbor attack
Army Major Kenneth Bergquist returned to Hawaii after attending the Mitchel Field 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 tell him his job was to assemble the equipment when it arrived. The commander in charge of defending Hawaii, General Walter Short, had a faint grasp of the weapons and tactics that Army technologists 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-270s became functional in July 1941 and, by November, Bergquist had only assembled a small team, but they were able to build a ring of four SCR-270-Bs around Oahu, with one unit in reserve. The radars were placed on the central north shore, Opana Point, in the northwest at the highest point- Mount Kaala, and one in the southeast corner at Koko Head. However, initially no real communications system or reporting chain was 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. Although communications were eventually improved, the chain of command was not. And by explicit order of General Short, the radar stations were to only be operated for four hours per day and to shut down by 7am each day. The one operational radar set in the Philippines, by contrast, was put on continuous watch in three shifts in response to the war warning sent to all overseas commands in late November.
Use on the morning of the Pearl Harbor attack
SCR-270 serial number 012 was installed at Opana Point, Hawaii on the morning of 7 December 1941, manned by two privates, George Elliot and Joseph Lockard. Though the set was supposed to shut down at 7 that morning, the soldiers decided to get additional training time since the truck scheduled to take them to breakfast was late. At 7:02 they detected 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, Kermit Tyler, who had arrived only a week earlier. He thought they had detected a flight of B-17s arriving that morning from the US. There were only six B-17s in the group, so this could not account for the large size of the radar echo. The officer had little grasp of the technology, the radar operators were unaware of the B-17 flight, and the B-17s had no IFF system, nor any alternative procedure for identifying distant friendlies such as the British had developed during the Battle of Britain. The Japanese aircraft they detected attacked Pearl Harbor 55 minutes later, precipitating the United States' formal entry into World War II.
The northerly bearing of the inbound flight was not passed along in time to be of use. The US fleet instead fruitlessly searched to the southwest of Hawaii, believing the attack to have been launched from that direction. In retrospect this may have been fortuitous, since they might have met the same fate as the ships in Pearl Harbor had they attempted to engage the superior Japanese carrier fleet, with potentially enormous casualties.
Aftermath
The radars on Oahu were put on round-the-clock operation immediately after the attack.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".
File:SCR-270 on Guadalcanal 1942.jpg|thumb|right|1942 photo of the SCR-270 utilized by the Marine Corps' Early Warning Detachment during the Battle of Guadalcanal.