F. W. Chesson						  File: GRR-4.HTM
fchesson@snet.net					   Rev: 27 Apr, 2001

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

  According to NARA documentation, although given Nomenclature Designation,
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 subsequently 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."

    This is indeed an interesting Wartime Radio Mystery!  Any further 
     information, or research approaches would be much appreciated!!

							Fred W. Chesson
Member: Antique Wireless Asso.				fchesson@snet.net