FD Fire Control Radar

Photograph of director with FD radar

National Archives #19-N-30722

Cropped by author

FD Mark 4


Wavelength 40 cm
Pulse Width 1.5 microsecond
Pulse Repetition Frequency    1640 Hz
Power 15-20 kW
Range 12,000 yards (11,000m) on 5" (127mm) shell splash
40,000 yards (37,000 meters) on bomber
12,000 yards (11,000 meters) on submarine
20,000 yards (18,000 meters) on destroyer
30,000 yards (27,000 meters) on battleship
A scope
Accuracy 40 yards (37 meters)
4 mils
Resolution 1500 feet (460 meters)
10 degrees
Production: 667 sets from 1941 to 1944

FD Mark 12


Wavelength 33 cm
Pulse Width 1.2 microsecond
Pulse Repetition Frequency    480 Hz
Power 100-110 kW
Range 45,000 yards (41,000 meters) on bomber
40,000 yards (37,000 meters) on battleship
A scope
Accuracy 15 yards (14 meters)/3 mils
Resolution300 feet/7degrees
Production: Used on Mark 37 directors for 5"/38 guns starting in 1944

The U.S. FD fire control radar was known in British service as the Type 285. It was similar to FC but had a larger antenna and gave altitude information. The antenna was a stabilized 6' by 6' (1.8m by 1.8m) double reflector with 2x4 dipoles and the display was an "A" scope with a 100,000 yard (91,000 m) range scale.

An improved version, the Mark 12, used the same antenna but an improved set. The Mark 12 also incorporated a Mark 22 low angle height finding radar. Its "A" scope used a 50,000 yard (45,000 m) range scale.


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Friedman (1981)
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