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The Elusive AN/GRR-4 "Secret Receiver".

According to the National Archives and Records Administration (NARA) documentation, Radio Set AN/GRR-4 may have barely existed. Only one unit was built for testing by the Ordnance Department at Aberdeen, MD and by the Johns Hopkins Applied Physics at Silver Springs, MD in July-August, 1944. Then the project was cancelled as of 20 September and a contract for 20 others, from Pacific Electronics of Spokane, Washington, was cancelled. The last document, of 4 November, indicates Signal Corps Supply Program of October 1, 1944 had no requirements for any GRR-4 equipment. However...see below!

As to functions, the GRR-4 and its R-92/ and R-93/ receivers, we may note the phrase "RCM Equip" in Pentagon letters of 19 and 27 June, 1 July, 22 August and 21 Sept., 1944. Can this indicate "Radio Counter-Measures" suggesting GRR-4 was a surveilance device covering a fairly wide frequency range, as indicated by the two R-92/ and R-93/ receiver units? Also note that Aberdeen Proving Ground was involved in the testing, possibly indicating a device for the operations of, or countermeasures for, remotely-controlled explosive devices (static mines/demolitions or else in signal-recon vehicles).

In in the information below, either the original GRR-4 (Project 210K at Wright Field) may have been revived as the Cold War flared up, or the old GRR-4 designation was re-applied to an entirely NEW device, perhaps for security purposes.

The 1946 Information:

JANP140 August 1946, as to security classification.  
AN/GRR-4 is classified "SECRET".  Cognizant service is "QCSIGO, E&T SVE, Radio Section".  Receiver R-92 
is "unclassified" while R-93 is "SECRET."  Cognizant Service is "AAF, AC/AS-4, Research & Eng. Div."

A 2009 Internet Report:

In a Texas Tech University Virtual Vietnam Library internet site, A First Cavalry Division report on battalion communications mentions the GRR-4 and GKR-5 receivers in use in Warning Nets. The AN/GKR-5 may well have been a data receiver used with intrusion sensor networks.

Fred W. Chesson (
18 Sept, 2009