The history of NIOC Hawaii N3J Department began on December 15, 1945 when the first Communications Supplementary Activity Detachment (COMSUPACT Det.) was established in Ohminato, Japan. When the Army evacuated the area in April 1946 the detachment was relocated to Yokosuka, and was designated as Communications Supplementary Activity (COMSUPACT) Yokosuka. On November 22, 1948, Navy Communications Unit 35 (NAVCOMMUNIT 35) was established and added a direction finding capability to COMSUPACT Yokosuka. A full rhombic antenna field was constructed in February 1949 to make the HFDF site fully operational. In 1950, Naval Security Group (NAVSECGRU) decided to shift control of the Pacific HFDF net to Yokosuka from Wahiawa, Hawaii.
To accommodate this change, NAVCOMMUNIT 35 was expanded to 38 officers and 392 enlisted and was located in renovated building F-68. The HFDF net was activated in Yokosuka on October 2, 1950. On January 15, 1960, the Naval Security Department (NSG) was commissioned as the U.S. Naval Security Group Activity (NSGA) Kami Seya. Naval Communication Facility (NAVCOMMFAC) at Kami Seya was relocated back to Yokosuka as Naval Communications Station (NCS) Yokosuka. On January 23, 1968, the USS Pueblo (AGER-2) was captured by the North Koreans. At the time of the attack, NSGA Kami Seya was in communication with the ship. There were six Sailors who were deployed on the USS Pueblo; they returned to NSGA Kami Seya 11 months later.
On August 1, 1969, all NAVSECGRU elements at Yokosuka were consolidated under one command structure and Naval Security Group Detachment Yokosuka, Japan, a detachment of NSGA Kami Seya, was established. In March 1971, most of the operational functions were moved from NSGA Kami Seya to NSG Detachment Misawa, Japan. On June 30, 1971, NSGA Kami Seya was downgraded to NSG Detachment Kami Seya and NSG Detachment Misawa was commissioned as NSGA Kami Seya. Activities at Kami Seya and Yokosuka became detachments of NSGA Misawa. On May 23, 1984, NSG Detachment Kami Seya was recommissioned as an NSGA. In January of 1989, NSG Detachment Yokosuka became a detachment of Kami Seya, once again.
On June 1, 1995, NSGA Kami Seya was closed permanently and NSG Detachment Yokosuka was recommissioned as an NSGA. On September 30, 2005, Naval Security Group was closed and many NSG Activities were closed as well. Those that remained open were recommissioned as Navy Information Operations Command (NIOC) on
October 1, 2005, including NIOC Yokosuka. On January 29, 2010, U.S. 10th Fleet (C10F) was recommissioned under Fleet Cyber Command. On October 1, 2014 NIOC Misawa, Japan was officially disestablished and the remaining Sailors were assigned to NIOC Yokosuka. The Sailors of NIOC Yokosuka, Japan have ensured the historic legacy of NSGA and NIOC Misawa endures by establishing the “NSGA and NIOC Misawa Honorary Bulkhead” inside the command.