AN/APR-27 MODS 1, 2, & 3


This installation of the AN/APR-27 was a temporary quick fix with the equipment being installed in the pilot’s map case and tying it into the auxiliary equipment wiring.  There are no external differences as this equipment shared the lower TACAN antenna (on the aft nose gear door).  When the AN/APR-27 was turned on normal operation of the TACAN was interrupted until the AN/APR-27 was switched off. 
The AN/APR-27 system was similar to the Singer CMR-312 system in that it was an audible warning only.  But whereas the CMR-12 alerted the aircrew to active radars in the vicinity, the AN/APR-27 searched for a SAM radar power-level change in the L-band command guidance frequency for guidance of the missile.   When the change would take place the system would audibly alert the aircrew so they could try and locate the missile and take evasive action.  It did not mean that the missile was aimed at them, nor did it give any indication of direction, just a warning that missiles were in the air with ground guidance. 

Note that at this point in time there were no external differences to the F-4 when this equipment was installed.  Only careful examination of the front cockpit would reveal the equipment installed where the map case once stood.  Kits were sent to the carriers that were in the war zone and they were installed while onboard the carrier.  The VF-14 Command Report (which was aboard CVA-42 USS Franklin D. Roosevelt) tells the story: "The APR-27 was installed during the latter segment of our combat tour.  This unit was a simple yet highly reliable item which is relatively maintenance free.  The map cases were removed from the front cockpit and the APR-27 was mounted in its place utilizing the 28 volt auxiliary jack as a power source.  The antenna installation … utilizes the lower TACAN antenna when the APR-27 is turned on. When the APR-27 is turned off, the TACAN goes back to normal operation.”

From the pilots standpoint it was well received: "At approximately the midpoint of this deployment, wiring diagrams and the "black box" for the APR-27 warning gear were available to the squadron.  The equipment has proven to be dependable in its operation and reliable in its warning.  All airplanes operating in the SAM environment should have this or similar equipment.”   

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1 - AN/APR-27 Mod 1 Hijacked the lower TACAN antenna when turned on.


 As part of Project Shoehorn (Mod 1 & Mod 2) a new home was found for the installation of the AN/APR –27 system.  Whereas before the equipment was installed in place of the pilots map case and used the TACAN antenna, this installation found a new home for the electronics and added a dedicated antenna just forward of the nose gear door. 

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1 - AN/APR-27 Mod 2 dedicated antenna


As part of Project Shoehorn (Mod 3) the AN/APR –27 system had a permanent installation in the same position as Shoehorn Mod 2; it was just part of a different EW suite.  

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1 - AN/APR-27 Mod 3 dedicated antenna

Revision History:
  •  17 MAR 2014 - Original Post