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In late 1943 the British decided to introduce the Mk III Identification Friend or Foe which required the use of an Interrogator to "read" the IFF responses. Another transmitter, receiver and aerial were required at each radar station to interrogate the Mk III IFF (possibly made by Bendix).  The American Hazeltine BL4 IFF Unit designed for the US Navy was used by the RAAF. A hurried installation program began in August/September 1943. The radar operator could distinguish on his screen if the aircraft was friendly or not.

Each aircraft was fitted with a simple short-wave transmitter which sent coded signals which could be interrogated by the ground station. IFF was sometimes referred to as secondary radar. When the IFF was triggered or interrogated by a primary radar it emitted a characteristic reply signal of its own. Hence the IFF in an aircraft produced a strong, tagged or labelled artificial echo.

RAAF aircraft had an explosive charge fitted to the IFF unit, which was triggered by an impact switch so that it exploded when the aircraft crashed to avoid the IFF falling into enemy hands. It could also be detonated manually by pressing two buttons simultaneously.

The detonator fitted to IFF equipment in Beaufighters housed three separate charges, about three inches in size, and was slotted into the front of the IFF equipment much as you slot a CD into its player. Corporal John Frederick Laverty (416686) was fined 2 Pounds for blowing up an IFF in a Beaufighter whilst testing the impact switch. Air crew were under instructions in Beaufighters to isolate the IFF just before landing to ensure that any heavy landing did not trigger the impact switch.

In May 1948 Mr A. W. Murray, the Bordertown powerhouse operator in South Australia, bought a Radar IFF Set from a disposal firm in Melbourne. Mr. Murray who owned a radio and electrical business, said that two of his radio mechanics found a live detonator in the IFF set. They exploded the detonator in the Powerhouse yard.

The Senior Air Staff Officer, North Western Area RAAF advised in a report dated 20 October 1944 to various operational squadrons in North Western Area that Japanese Radar may be triggering the Allied IFF transponders. The Japanese had two types of radar, in both of which the upper frequency limits overlapped the lower limits of the IFF Mark III band.

Field Unit 2 of Section 22 found that IFF's were being left on until about 10 minutes from the Japanese target. During one flight to Davao on 18 September 1944, the IFF's were constantly being triggered by enemy signals, thus providing the enemy better warning of the arrival of Allied aircraft than their radar.

Field Unit 9 of Section 22, also encountered a number of incidents where Japanese radars triggered their Aircraft's ABK IFF transponder.

A report by Coast Artillery reported another issue, this time for returning aircraft, that 50 percent of returning SWPA planes did not turn their IFF back on when they returned from a mission over enemy territory. Then of course you needed to turn IFF off again immediately prior to landing to prevent accidental operation of the detonators on the IFF.



"Radar Yarns"
edited by Ed Simmonds & Norm Smith

The Army Air Forces in World War II
Plans & Early Operations January 1939 to August 1942
Section 1: Earl Heritage

The Advertiser (Adelaide, SA), Detonator found in Radar Set, 24 May 1948

SCR-595-A or SCR-595-AZ Navy Model ABK of ABK-1, Aircraft Radio Receiving Equipment

IFF -- Identification Sets

IFF Identification Friend or Foe - shows photo of Mk III IFF



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This page first produced 2 January 2016

This page last updated 04 March 2020