Early-Warning Radars (part 3)

Jug Handle and Boston Hill Radars

By 1954, it had become apparent that the L- and S-band ground control of intercept (GCI) radars used in the Cape Cod System were showing an unacceptable amount of clutter on their displays. At the same time, the ongoing development of UHF airborne early-warning (AEW) radar systems equipped with moving-target indication was demonstrating the advantages of radars operating at longer wavelengths. GCI radars operating at a longer wavelength appeared to address all of the problems that beset those at L- and S-band. However, the horizontal aperture of the rotating radar antenna would have to be larger in proportion to the wavelength in order to maintain the same angular resolution in azimuth. For the desired capabilities, the antenna had to be 120 ft wide by 16 ft high, but because its mechanical tolerances could be less stringent than those of an L-band antenna (because of its lower frequency), it was not expected to be a great challenge to construct.

Jug Handle Hill radarGCI radar at Jug Handle Hill. Picture is used with the permission of The MITRE Corporation (copyright © The MITRE Corporation; all rights reserved).

The new UHF radar with the desired capabilities was designated the AN/FPS-31. A site was chosen on Jug Handle Hill in West Bath, Maine, which made the AN/FPS-31 the counterpart of shoreline GCI radars at South Truro, Massachusetts, and Montauk Point, New York.

The original design called for the rotating antenna to be carried on sets of bogie wheels at the ends of a three-armed spider that rolled on a smooth, level circular track at the top of the tower. This system caused trouble from the start. The track had not been made sufficiently smooth, and the wheels soon wore out. Pressure to get the AN/FPS-31 radar into operation led to the adoption of a scheme whereby the entire rotating assembly rode upon a large central ball. Although this modification presented its own challenges, the mechanical problems were eventually worked out and reliable operation of the large rotating antenna was achieved. The experience Lincoln Laboratory gained in solving these problems paid off in the subsequent successful mechanical designs of the counter-countermeasure (CCM) radar Mark I, the angle-tracking antenna of the Millstone radar, the AN/FPS-49 tracking radars, and others.

The AN/FPS-31 radar began to operate in October 1955. During the early checkout of the radar, echoes resembling returns from storms were observed. These turned out to be echoes from the aurora borealis—the Northern Lights. The radar was so sensitive that it could detect backscatter from the aurora high in the earth's atmosphere, far to the north.

In 1956, following assignment of the Jug Handle Hill radar to the SAGE Experimental Subsector, Lincoln Laboratory began work on an experimental advanced UHF radar to be used, in part, to evaluate new counter-countermeasure techniques. The experimental radar, designated as the CCM radar Mark I, was of particular importance because the UHF frequency range was to be employed in radar jammers then under development by the Soviet Union.

Boston Hill radarUHF radar on Boston Hill in Andover, Massachusetts.

Design of the antenna and tower started in September 1956. In February 1957, an area on top of Boston Hill in North Andover, Massachusetts, was leased for the radar. Construction began immediately and the radar was first powered up in August 1958.

The main purpose of the Boston Hill radar was to serve as an instrumentation system for testing automatic detection and tracking of distant objects at a sufficiently high data rate to serve as an input to the SAGE system. The experimental work also emphasized measures designed to enable the radar to operate both actively and passively in a jamming environment.

 

Texas Towers

The final link in the early-warning network protecting the perimeter of the United States was a set of radar installations located in the Atlantic Ocean. In 1952, Lincoln Laboratory first suggested that permanent platforms be erected in shallow water at selected points along the Continental Shelf to provide a seaward extension of the radar warning system. These permanent marine radar stations were not inexpensive to build; nonetheless, they were both cheaper and more effective than radar picket ships, which were also employed at various times during the SAGE development.

Successful use of such platforms off the Gulf Coast for oil-drilling operations (thus the nickname Texas Towers) made the plan seem feasible. After thorough study, the Air Force decided to adopt the Lincoln Laboratory suggestion. By January 1955, plans were being laid for the construction and installation of radar platforms off the coasts of Cape Cod, Massachusetts, and Long Island, New York.

The feasibility of long-distance communications was one of the main considerations in evaluating the practicality of a fixed marine radar station. Other radar stations used telephone lines and microwave line-of-sight radio for communications. The ocean-based towers, more than 100 mi offshore, could use neither. The conventional solution, transatlantic cable, was too expensive for the number of circuits needed.

The solution to the long-range communications problem came from Lincoln Laboratory's development of UHF tropospheric scatter communication. In fact, the Texas Towers pioneered the use of UHF tropospheric scatter propagation for overwater communication.

The UHF link between each tower and its direction center provided the equivalent of 72 four-wire telephone channels. Communication between each tower and aircraft for interceptor control was by line-of-sight UHF radio.

Standing on 10 ft diameter steel caissons driven into the sea floor, each Texas Tower was a half-acre steel island elevated 67 ft above the sea. The uppermost of the four decks carried three radomes, housing an AN/FPS-3 search radar and two AN/FPS-6 height-finding radars. The deck also held identification-friend-or-foe (IFF) equipment, a Mark X beacon, and four AN/FST-2 digital data transmitters. The remaining three decks housed the personnel and maintenance equipment, control equipment, water, and fuel. Fifty Air Force personnel, two meteorologists, and twenty civilians operated each station.

Map of Texas Tower radar sites

The sites of the Texas Tower radars are shown at the left. Map courtesy of the Air Defense Online Radar Museum, www.radomes.org/museum/.

The Air Force had approved five sites, but only Texas Towers 2, 3, and 4 were actually built.  On January 15, 1961, Texas Tower 4 was destroyed by a winter storm.  Tragically, none of the 28 airmen and civilian contractors who were manning the station survived. Below left are photos of Texas Tower 2 on Georges Shoal, Massachusetts. Tower 2 photograph on the right is also courtesy of the Air Defense Online Radar Museum.

Texas Tower radar site Texas Tower radar site

 

Back to part 1: Early-warning radars and the DEW Line

Back to part 2: MIT Lincoln Laboratory develops UHF early-warning radar


Adapted from E.C. Freeman, ed., Technology in the National Interest, Lexington, Mass.: MIT Lincoln Laboratory, 1995.

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