U.S. Navy Shipboard Radars XAF

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The “XAF”, an experimental radar that resulted from several years’ technical progress by the Naval Research Laboratory (NRL), was constructed in 1938, following a late February decision to install a radar set on a major warship. Operating at 200 megacycles (1.5 meter wavelength) at a power of 15 kilowatts, the XAF featured a “bedspring”-like antenna about 17 feet square. This was mounted in a rotating yoke that allowed it to scan around the horizon, and to elevate for what was hoped would be improved aircraft detection. This large antenna and yoke had to be strong enough for sea service, while remaining as light as possible to avoid excessive topside weight. Accordingly, the Brewster Aeronautical Corporation (then also building the Navy’s first monoplane shipboard fighter, the F2A “Buffalo”), was given the job of fabricating a suitable duralumin structure. The XAF’s transmitter, receiver and other equipment were made by NRL.

When development and construction were complete, the XAF was installed on the battleship New York. This work, with the antenna mounted atop the pilothouse (where it displaced a large rangefinder — moved to the top of the ship’s Number Two 14-inch gun turret) was completed in December 1938. During nearly three months of constant operation, averaging almost twenty hours daily as New York participated in winter maneuvers and battle practice in the Caribbean, the XAF’s performance and reliability exceeded expectations. It detected aircraft up to 100 nautical miles (nm) away and ships out to 15 nm. The radar was also employed for navigation and in gunnery practice, spotting the fall of shot and even tracking projectiles in flight.

At the conclusion of these tests, New York’s Commanding Officer recommended installation of radar in all aircraft carriers (whose vulnerability to surprise air attack was very well-understood), while the Commander of the Atlantic Squadron commented “The XAF equipment is one of the most important military developments since the advent of radio …”. Later in 1939, the XAF was reengineered and placed in production by the Radio Corporation of America. Designated CXAM, six of these production models were delivered in 1940 and installed on an aircraft carrier, a battleship and four cruisers. An improved version, CXAM-1, with a simplified antenna, was produced in greater numbers. By the time the United States entered World War II in December 1941, the use of radar in the U.S. Navy was rapidly expanding.

The XAF radar’s antenna survived World War II as a historic artifact. For several decades in the middle and later Twentieth Century it was exhibited in Willard Park, close to the Washington Navy Yard’s waterfront. However, the outdoor environment contributed to serious deterioration in the antenna’s condition, and it was placed in storage in the mid-1990s. In May 2008 it was loaned to the Historical Electronics Museum, located in Linthicum, Maryland, where it is to be restored and again placed on public exhibit.

Source note: Most of the information in this text is taken from the following sources: Captain L.S. Howeth, USN: History of Communications-Electronics in the United States Navy, Chapter XXXVIII (Washington, D.C., 1963); and Norman Friedman: Naval Radar (Greenwich, England, 1981).

bron: http://www.history.navy.mil/photos/weap-sen/radar/us/xaf.htm