"Krug" System (THICK EIGHT)
System Overview and Nomenclature
Krug (Russian: Krug, meaning circle) is the conventional name used in open sources for a Soviet strategic high‑frequency direction‑finding and electronic reconnaissance network developed beginning in the early 1950s. It was designed to detect, fix, and analyze radio emissions associated with NATO maritime and air operations. Some Western open sources apply the reporting name THICK EIGHT to this network. This is distinct from the unrelated 2K11 Krug surface‑to‑air missile system designated by NATO as SA‑4 GANEF.
Mission and Target Set
The network’s mission was to provide long‑range radio‑technical reconnaissance of adversary forces by intercepting and triangulating radio emitters, with emphasis on carrier strike group communications, strategic bomber and reconnaissance aviation support nets, and other high‑value emitters. Over time, the target set came to include communications associated with platforms such as the SR‑71 reconnaissance aircraft and NATO maritime patrol and strike assets, as well as command‑and‑control circuits that enabled correlation of activity and movement.
Architecture and Components (as reported in open sources)
Open‑source accounts describe the system as comprising 12 strategic electronic reconnaissance complexes, 8 separate radio direction‑finding stations (often abbreviated OPPU in Russian sources) distributed around the USSR’s periphery, and 4 overseas collection centers located in Lourdes (Cuba), Cam Ranh (Vietnam), Rangoon (Burma), and Ulaanbaatar (Mongolia). These figures and locations are reported in secondary sources such as GlobalSecurity; they are not corroborated by publicly released primary Soviet or Russian documentation.
Site Infrastructure and Technical Characteristics
Krug sites are characterized by very large circularly disposed antenna arrays for high‑frequency direction finding, commonly referred to in the West as CDAA or elephant cage arrays. Typical installations consist of dozens of vertical radiating elements arranged in a circle hundreds of meters in diameter, a central goniometer and processing building, power and communications support, and buried or overhead trunk lines connecting to higher‑level analysis centers. Coverage was in the high‑frequency spectrum (approximately 2–30 MHz), with direction finding by amplitude or phase comparison at a single site and geolocation refined through multi‑site triangulation and time‑difference‑of‑arrival techniques. Specific performance parameters remain classified; open-source descriptions generally place single‑site bearing accuracy on the order of degrees, improving to tactically useful fixes when multiple stations are used concurrently.
Organizational Control
During the Soviet period, strategic signals and electronic intelligence collection, including long‑range HF/DF, fell under the Main Intelligence Directorate of the General Staff (GRU), specifically the 6th Directorate responsible for radio‑electronic intelligence. Subordinate field elements were organized as separate radio emission direction‑finding units and nodes. After 1991, Russian military signals intelligence functions continued under the GRU within the Armed Forces, with numerous reorganizations; detailed current command relationships for legacy Krug‑designated facilities are not publicly disclosed.
Status of Overseas Sites
Lourdes, Cuba: Operated from the 1960s as a major Soviet/Russian signals intelligence center; closure was announced by Russia in 2001, and there is no authoritative public confirmation of its reactivation as of 2024. Cam Ranh, Vietnam: The USSR/Russia maintained a military presence, including intelligence elements, under agreements dating from 1979; Russian forces fully withdrew by 2002, and there is no public evidence of a restored permanent Russian SIGINT site thereafter. Mongolia (Ulaanbaatar): Soviet forces withdrew from Mongolia by 1992; there is no confirmed ongoing operation of Soviet‑era SIGINT centers under Russian control. Burma (Rangoon): Authoritative open sources do not substantiate the existence of a Soviet/Russian SIGINT center in Rangoon; widely cited reporting instead concerns Chinese‑linked facilities on the Coco Islands. Consequently, only Cuba and Vietnam are documented as former overseas Soviet/Russian SIGINT hubs tied to this mission set, with operations terminated by the early 2000s.
Domestic and Perimeter Stations
The perimeter stations attributed to Krug were positioned to exploit HF propagation and maximize baselines for triangulation around the USSR’s borders and littorals. Their geospatial signature is the large circular antenna field with a central building and associated support infrastructure. Many such sites, including in the territory of the Russian Federation and other former Soviet republics, remain visible in satellite imagery due to their size. Open sources indicate that some were dismantled or fell into disuse after the early 1990s; the extent of refurbishment or continued operation at specific locations is not documented in authoritative public records.
Integration with Broader Soviet/Russian Reconnaissance
Krug‑type HF/DF collection complemented other reconnaissance and surveillance systems. It provided emitter geolocation and activity pattern analysis that could cue or be fused with space‑based maritime reconnaissance (for example, the Soviet ocean surveillance system commonly known as Legenda) and with theater reconnaissance assets and conventional radar networks. The combination allowed correlation of communications activity with platform movement, enhancing indications and warning and operational‑level situational awareness.
Listed Units and Military Unit Numbers
The following designations are cited in open sources as separate radio emission direction‑finding units or a central communications element: military unit 34575 (title not specified in the provided data), 50th Separate Radio Emission Direction Finding Unit (military unit 14145), 230th or 811th Separate Radio Emission Direction Finding Unit (military unit 34630; the dual numbering suggests reorganization or alternate designations in different periods or sources), 309th Central Radio Emission Direction Finding Communications Unit (military unit 34608), and 874th Separate Radio Emission Direction Finding Unit (military unit 48260. Publicly available materials do not provide consistent, authoritative mappings of these unit numbers to specific Krug sites or current garrison locations. Without official disclosure, further details on their present composition, locations, or equipment cannot be confirmed.
Operational Status Since 1991
Foreign components associated with the Cold War‑era network, notably in Cuba and Vietnam, were closed by 2001–2002. Within the former USSR, many large HF/DF arrays persisted physically but saw variable levels of maintenance. Russia maintains strategic SIGINT capabilities, including HF/DF, under modernized structures and equipment; however, open sources do not provide authoritative confirmation that a legacy Krug network, as a discrete 12 plus 8 plus 4 system, continues to operate today. The assertion that the original network remains in service cannot be substantiated from public records; any current operations at former sites would reflect contemporary Russian SIGINT programs rather than the unchanged Soviet‑era system.
Deconfliction with Similarly Named Systems
Krug in this report refers to an HF/DF and electronic reconnaissance network and should not be confused with 2K11 Krug, a Soviet medium‑range surface‑to‑air missile system with the NATO designation SA‑4 GANEF. The shared Russian name has caused frequent misattribution in non‑specialist sources.
Information Gaps and Verification Needs
Several details remain unverified in public sources, including the exact enumeration and locations of the 12 strategic complexes and 8 OPPU, definitive confirmation of a Burmese site at Rangoon, and the current status of specific units listed with military unit numbers. Verification would require official disclosures, declassified primary documentation, or unambiguous contemporary evidence such as clear indications of maintained antenna fields, active security perimeters, and recent procurement or garrison orders identifying the units and their equipment.
Summary Assessment
Krug was a Soviet strategic HF/DF and electronic reconnaissance network developed in the early Cold War to monitor and geolocate Western maritime and aviation communications. Open sources depict a multilayered architecture that included large circular HF/DF arrays across the USSR and several overseas collection centers. The foreign elements were closed by the early 2000s, and while some physical infrastructure of domestic sites remains, there is no authoritative public confirmation that the Soviet‑era network continues to operate as such. Russia retains robust SIGINT capabilities, but continuity under the Krug designation and the specific structure described in Cold War literature cannot be verified from publicly available information.