CXAM1 Air Search Radar

Photograph of CXAM radar antenna

National Archives #19-N-32465-B


Wavelength 1.5 m
Pulse Width 3 microsecond
Pulse Repetition Frequency   1640 Hz
Scan rate 5 rotations per minute
Power 15 kW
Range 70 nautical miles/130km (bomber)
50 nautical miles/90km (fighter)
16 nautical miles/30km (battleship)
12 nautical miles/20km (destroyer)
17' square 6x6 dipole "mattress" array
A scope
Accuracy 300 yards (270m)
3 degrees
Resolution 600 feet (180m)
3 degrees
Weight 5000 lbs (2300kg), of which 1200 lbs (500 kg) was antenna
6 CXAM by late 1940
14 CXAM-1 by 1942

The CXAM1 naval air search radar was one of the first to see widespread use, being mounted on a few capital ships by 1942. It provided no altitude information and was heavy and bulky, but it revolutionized naval air defense.

The radar was a development of XAF, which was developed by the U.S. Naval Research Laboratory and first tested in a warship in 1938. It used a large rotating mattress antenna (17' square and consisting of 6x6 dipoles) and proved capable of air and surface search and even of spotting the fall of shells. The first production sets were ordered in October 1939. By 1940 these had been fitted to California, Yorktown, Chicago, Chester, Pensacola, and Northampton. By the time war broke out, additional sets were installed in the U.S. Navy's other carriers, five other battleships, and in the cruiser Augusta.

A curiosity of this radar was that its wavelength was short enough to restrict it to line of sight, but long enough for the technology of the day to modulate it.  Thus, towards the end of the war, the radar doubled as a talk-between-ship communications system.


Buderi (1998)

Friedman (1981)

Guerlac (1987)
Hezlet (1975)
Naval Historical Center (accessed 2009-6-6)

Roberts (1982)

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