HFDF Network (AN/GRD-6)

In the mid-1950s, the U.S. Naval Research Laboratory (NRL) developed the AN/GRD-6 system as the standard for Project Boresight HFDF networks.

Developed in 1958 by the US Naval Research Laboratory (NRL), the AN/GRD-6  system was comprised of two arrays and associated electronics. The high HF array, depicted here, consisted of eight monopole sleeve antennas  and eight, terminated,  folded monopoles for the Low HF band, arranged in two separate circles.

It had two separate 8-element arrays for covering the high and low bands of the HF spectrum. The high-band monopole elements were called self-sustaining sleeve antennas.  AN/GRD-6 systems were installed in 1956-58 at Kami Seya, Adak Alaska, Kodiak Island Alaska, Finegayan Guam, Midway Island, and Skaggs Island in California, as part of the Pacific HFDF Network and at Homestead in Florida, Galeta Island in Panama, Bermuda, the Azores, Edzell in Scotland, and Hafnir, near Keflavik in Iceland, as part of the Atlantic HFDF Network. By 1960, the worldwide, quick-reaction Boresight project was fully operational with most NSG stations equipped with AN/GRD-6 systems. During the Cuban Missile Crisis in October 1962, Boresight HFDF stations were able to track nearly all Soviet submarines at sea by monitoring their burst transmissions.

AN/GRD-6 system electronics. Pictured represents one half of the required equipment since the high and low arrays each had their own dedicated electronics but sharing the bearing sender and teletypewriter. See the functional block diagram below.  The system consisted of the following components: Azimuth Indicator IP-272, Teletype Coder KY-168, Switch Box SA-430, Receiving Group Control C-1647 and Radio Receiver R-665.

A Marine Corps unit arrived at Kami Seya around July 1956. It was formed as the 1st Special Communications Platoon of the Headquarters Battalion based at the USMC HQ. It had an authorized strength of 43 Marines, including officers and enlisted men. They were all R Branch Morse intercept specialists. Nearly all of them worked in Sections 2 and 4 in the Tunnel. In April 1958, the platoon was redesignated Sub-Unit 5 of Company G, Headquarters Battalion, USMC HQ. It became Company E of the Marine Support Battalion on 1 October 1961.

An Army Security Agency (ASA) DF detachment from the 12th Field Station at Chitose arrived at Kami Seya in late 1959 and began operating in January 1960. They worked out at the GRD-6 site, in the DF operations building located between the low-band and high-band antenna systems; they reported directly to Chitose.

Disappearance of USAF RB-50G

RB-50G ELINT Aircraft

The Communications Intelligence (COMINT) collected at Kami Seya included Soviet reactions to USAF and US Navy reconnaissance flights along the Soviet coast-line, and sometimes into Soviet airspace. In September 1956, for example, the Kami Seya station intercepted Soviet communications concerning the disappearance of a USAF RB-50G ELINT aircraft (No. 47-133) near Vladivostok. This included HF Morse and voice communications between Soviet radar tracking stations and tracking data on Soviet fighters. On 12 and 14 September, two and four days after the disappearance, Kami Seya reported details of overflights of the search area by IL-28 reconnaissance aircraft, and on 13 September it also reported that there were indications that at least one Soviet submarine was operating in the vicinity.

Staff Sergeant Donald G. Hill, USAF Airman 2nd Class Earl W. Radlein, USAF

By the end of the 1950s, the Kami Seya station had functionally subsumed NCU-38 in central Tokyo. It formed its own Direct Support Unit, later called the 5th Division, for providing personnel and logistical support for US Navy ship-based and airborne SIGINT collection operations. It also maintained a Signals Analysis Laboratory, later also called 30 Department, which effectively replaced Navy Communications Unit (NCU) 38’s Signals Analysis Center. By the late 1950s, the Direct Support Units were generally equipped with magnetic tape recorders, replacing the wire recorders that were the centerpiece of NCU-38’s Signals Analysis Center.

Betrayers of the Trust

In June-July 1960, two NSA employees, William H. Martin and Bernon F. Mitchell, defected to the Soviet Union. They had served together at the NSG stations at Yokosuka and Kami Seya in 1951-54, where they became firm friends, and later at NSA HQ at Fort Meade (1957-59). Martin also worked as a civilian at an Army SIGINT station in Japan in 1955-56. At a press conference in Moscow on 6 September, they described the organization and operations of the NSA and its methods of SIGINT targeting of the Soviet Union and the People’s Republic of China. They said that the practice to which they objected most was the deliberate violation by US ferret aircraft of the airspace of other countries in order to detect and record electronic data. They were familiar with this provocative activity from their period at Kami Seya, which was tasked with monitoring the frequencies used by radar reporting stations of the target country, i.e., the Soviet Union or Communist China, whenever a reconnaissance flight was scheduled. At the same time, radio direction finders would tune in on these frequencies to seek out the locations of the radar reporting Stations.

Nautilus Institute for Security and Sustainability, 23 December 2015
David P. Mowry, Betrayers of the Trust, (Center for Cryptologic History, National Security Agency, Fort George G. Meade, Maryland)
Michael L. Peterson, Maybe You Had to Be There
James Bamford, ‘Body of Secrets: Additional Backnotes