SHORAN
From Wikipedia, the free encyclopedia
SHORAN is an acronym for SHOrt RAnge Navigation, a type of electronic navigation and bombing system with a precision radar beacon used in the B-26 and B-29 bomber aircraft during the Korean War.
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[edit] Origin
During World War II the United States Army Air Forces realized a need for a navigation system that would operate in poor weather conditions over European theatres. An early model was demonstrated in the United Kingdom in 1943, and showed potential. Unfortunately, the entire design team was killed when their plane crashed on its return trip to the United States. Scribbled notes and sketches were all that remained of the system's design, and redeveloping the specifications was a frustrating long-term project. It was built, but due to the system's relatively short range of approximately 300 miles, it was not used in many aircraft during the war. It did see some action over Italy and proved to be very helpful in bombing situations where visual acquisition of targets was impossible. Stuart William Seeley, the scientist who invented SHORAN received a Magellanic award for his work in 1960.[1]
[edit] Structure
SHORAN, which operates at 300 MHz, requires an airborne AN/APN3 set and two AN/CPN2 or 2A ground stations. The equipment onboard the aircraft includes a transmitter, a receiver, an operator's console and a K-1A model bombing computer. The transmitter sends pulses to one of the ground stations and the system calculates the range in statute miles by clocking the elapsed time between transmitter pulse and the returned signal. The system was intended for use in navigation, but it became obvious that it would work well for blind targeting during bombing runs in poor visibility. The setup made up of the K-1A bombing computer combined with the navigation system was the first SHORAN. The SHORAN system is designed so that as the aircraft faces the target, the low-frequency station should be on the left, and the high-frequency station is on the right. This allows the computer to triangulate the two stations and the target.
[edit] Limitations
The limitations of SHORAN included:
- A maximum range of 300 statute miles and a clear radio path
- No more than 20 aircraft may contact a pair of stations at once
- Complex parameter calculations made prior to flight cannot be changed during the bomb run
- Station angle must be between 30 degrees and 150 degrees, and the exact geographical position of each of the two ground stations and the target must be known
- The 100 mile ambiguity must be recognized and taken into account
- There are only four possible approaches to any one target, all predefined by the geometry of the system
- Because the system is line-of-sight limited, the plane must fly at altitudes above 14,000 feet and sometimes as high as 16,000 feet, depending on local geography. These altitudes are not easily made by a fully-loaded bomber. The engines are worked to capacity.
- Only stationary targets can be attacked
- The use of statute miles instead of nautical miles may be confusing in some situations
[edit] High Tech Bombing in Korea
Little new top-of-the-line technology was used in Korea, but SHORAN was an exception. B-26 planes were first equipped with the system in January, 1951, and first carried it into battle the following month.
Some problems immediately recognized were that ground stations tended to be too far from the targets, the ground and aircraft equipment was not maintained properly, few technicians knew how to work the equipment, and operators were too unfamiliar with Korean geography to use the system to the fullest extent.
Changes were made and by June of 1951 ground stations were located in more useful areas, such as islands and mountaintops, and training of operators and technicians familiarized them with the system. By November 1952 these changes had developed SHORAN into a reliable accurate blind-bombing system which was used by B-29 and B-26 aircraft for the remainder of the war.
