The Naval Security Group (NSG) was less involved in the Korean War than the Army Security Agency (ASA) or U.S. Air Force Security Service (USAFSS). As an NSA history of U.S. SIGINT activities has stated:

The DPRK had no blue-water navy, and [the NSG] was not concerned with the small collection of DPRK coastal patrol craft. The organization concentrated instead almost entirely on the Soviet navy in the Pacific, to determine what moves, if any, the Soviets would make toward the U.S. presence on the Korean Peninsula. (1)

01
NCU-35, Yokosuka, January 1951 Source: Photo by Bob Torstenson

At the beginning of the war, the NSG had a single intercept station in Japan, at Yokosuka, maintained by Navy Communications Unit Thirty-Five (NCU-35), with a HF DF and radio finger-printing (RFP) facility at nearby Kannon Zaki. Another DF site was situated at Tengan (NCU-37) in Okinawa. NCU-35 became the Net Control station for the NSG’s Pacific HD DF network on October 2, 1950. There were 430 personnel in NCU-35 in July 1950. (2) The commander in June 1950 was Commander Daniel W. (‘Pop’) Heagy, who was succeeded by Captain Wesley Wright a few months later. (3) As noted above, the Yokosuka station became host to the new AFSA Field Activity, Far East (FAFE) around September 1950, while NCU-35 provided nearly all its personnel. (4) In addition, because of the lack of North Korean naval traffic, some NCU-35 intercept operators ‘worked with ASA Far East on Korean collection’. (5)

02
US Navy Signal Analysis Center, NCU-38, Tokyo Source: Photo by Bill Lockert, ‘Yokosuka, Japan NCU-38, 1951-1956; Tokyo, Japan NCU-38, 1957-59

When Chinese forces crossed the Yalu River and entered the Korean War in October/ November 1950, the NSG personnel at Yokosuka feared for the safety of their own activity. One veteran recalled the news of the Chinese entry caused ‘an eerie feeling and called back memories of Pearl Harbor.’ He has said that, ‘since we were at the entrance to Tokyo Bay, we were in a position which could easily be attacked’. The sailors spent more than 24 hours ‘burning sensitive material’. Soon after, members of the unit were given ‘basic combat training’ and ‘were advised we would defend our station long enough to destroy equipment and material then fall back into the hills’. (6)

03
US Navy Signal Analysis Center, NCU-38, Tokyo Source: Photo by Bill Lockert, Yokosuka, Japan NCU-38, 1951-1956; Tokyo, Japan NCU-38, 1957-59

Both the Yokosuka and Kannon Zaki sites suffered from space constraints, and construction of a replacement site for both intercept and DF activities at Kami Seya, about 18 miles to northwest of Yokosuka, began in 1951. The Kami Seya station became operational in late 1952, and was commissioned on December 12, 1952. (7)

04
US Navy Signal Analysis Center, NCU-38, Tokyo Source: Photo by Bill Lockert, Yokosuka, Japan NCU-38, 1951-1956; Tokyo, Japan NCU-38, 1957-59

Another NSG unit, NCU-38, was set up at Yokosuka in 1951. It moved to Far East Command (FEC) in Tokyo in 1957, where it remained until 1959. It maintained a Signal (Wire Recorders) Analysis Center while it was located at both Yokosuka and FEC. It also served as a Direct Support Unit, providing the personnel and logistical support for US Navy shipbased and airborne SIGINT collection operations. (8) Four Martin P4M-1Q Mercator longrange ELINT aircraft were assigned to NCU-38 in October 1951. They constituted a Special Electronics Search Program which provided SIGINT and ECM support to the Pacific Fleet. (9)
Footnotes:
(1) Thomas R. Johnson, American Cryptology during the Cold War, 1945-1989. Book I, p. 51.
(2) Jay R. Browne, ‘Early Development’, p. 26; Jay R. Browne, ‘Kami Seya Update P-2’, p. 1; Richard S. Katzenberger, ‘1945-1946’, Closing Ceremony NSGA Hanza: 53 Years of Faithful Service, The Worldwide CT Community and Our Naval Security Group, p. 5; correspondence from George McGinnis, 16 August 1999; and Roland C. Delmotte, ‘Tengan, Okinawa’.
(3) Austin (‘Jack’) Rutledge, ‘COMM UNIT #35’, NCVA Cryptolog, Spring 1995, p. 5; and Matthew M. Aid, ‘American Comint in the Korean War (Part II): From the Chinese Intervention to the Armistice’, Intelligence and National Security, (Vol. 15, No. 1), Spring 2000, p. 19.
(4) Matthew M. Aid, ‘US Humint and Comint in the Korean War’, p. 50.
(5) David A. Hatch and Robert Louis Benson, ‘The Korean War: The SIGINT Background’.
(6) Austin (‘Jack’) Rutledge, ‘COMM UNIT #35’, p. 5.
(7) George McGinnis, ‘Early Kami Seya’, pp. 2-3; and Donald C. Polk, ‘Kami Seya in the Mid 1950s’, NCVA Cryptolog, (Vol. 18, No. 4), Fall 1997, pp. 8-9.
(8) Bill Lockert, ‘Yokosuka, Japan NCU-38, 1951-1956; Tokyo, Japan NCU-38, 1957-59’, The Worldwide CT Community and Our Naval Security Group, at http://www.navycthistory.com/tokyo_ncu-38_intro.html.
(9) ‘Fleet Air Reconnaissance Squadron One’, Declassified US Government Internal Documents on the Central Intelligence Agency (CIA), at https://archive.org/stream/CIADocuments/CIA-530_djvu.txt.

Source: Nautilus Institute, Special Report, 24 December 2015